ensure BunString::toStringRef increases ref count

[dylan-conway]

What does this PR do?

Discovered after webkit upgrade

How did you verify your code works?

manually

[robobun]

❌ @dylan-conway, your commit 360925b has 13 failures in #4894:

test/regression/issue/ctrl-c.test.ts - illegal instruction at address 0x7ff81cd5a37b on 🍎 13 x64

test/cli/install/bun-install.test.ts - 1 failing on 🐧 20.04 x64

test/cli/install/bun-install.test.ts - 1 failing on 🐧 22.04 x64

test/cli/install/bun-install.test.ts - 1 failing on 🐧 20.04 x64-baseline

test/cli/install/bun-install.test.ts - 1 failing on 🐧 22.04 x64-baseline

test/js/web/fetch/fetch.tls.test.ts - 1 failing on 🍎 13 aarch64

test/cli/run/require-cache.test.ts - 1 failing on 🪟 x64-baseline

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🍎 13 aarch64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🪟 x64-baseline

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🍎 14 aarch64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🪟 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 12 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 22.04 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 20.04 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🍎 13 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🍎 14 x64

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 22.04 x64-baseline

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 12 x64-baseline

test/js/node/test/parallel/http2-server-rst-before-respond.test.js - 1 failing on 🐧 20.04 x64-baseline

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🍎 13 aarch64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🍎 14 aarch64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 22.04 x64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 20.04 x64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 12 x64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🍎 13 x64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🍎 14 x64

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 22.04 x64-baseline

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 12 x64-baseline

test/js/node/test/parallel/http2-large-write-close.test.js - 1 failing on 🐧 20.04 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🍎 13 aarch64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🪟 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🍎 14 aarch64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🪟 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 12 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 22.04 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 20.04 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🍎 13 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🍎 14 x64

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 22.04 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 12 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints.test.js - timeout on 🐧 20.04 x64-baseline

test/js/bun/http/fetch-file-upload.test.ts - 1 failing on 🪟 x64-baseline

test/js/bun/http/fetch-file-upload.test.ts - 1 failing on 🪟 x64

test/cli/hot/watch.test.ts - 1 failing on 🪟 x64-baseline

test/cli/hot/watch.test.ts - 1 failing on 🪟 x64

test/js/bun/http/bun-serve-static.test.ts - 2 failing on 🍎 13 aarch64

test/cli/install/registry/bun-install-registry.test.ts - 1 failing on 🪟 x64

test/cli/watch/watch.test.ts - 2 failing on 🪟 x64

test/cli/watch/watch.test.ts - 2 failing on 🪟 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🍎 13 aarch64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🪟 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🪟 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🍎 14 aarch64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 22.04 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 20.04 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 12 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🍎 13 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🍎 14 x64

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 22.04 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 12 x64-baseline

test/js/node/test/parallel/http2-compat-write-early-hints-invalid-argument-type.test.js - 1 failing on 🐧 20.04 x64-baseline