Fix parsing for zone offset seconds #3520

Job	Run time
rust_msrv (ubuntu-latest)	3m 2s
no_std (ubuntu-latest, thumbv6m-none-eabi)	12s
timezones (ubuntu-latest, ACST-9:30)	1m 21s
no_std (ubuntu-latest, x86_64-fortanix-unknown-sgx)	13s
rust_versions (ubuntu-latest, stable)	1m 7s
timezones (ubuntu-latest, EST4)	1m 23s
timezones (ubuntu-latest, UTC0)	1m 24s
timezones (ubuntu-latest, Asia/Katmandu)	1m 28s
alternative_targets (ubuntu-latest, wasm32-unknown-emscripten)	14s
rust_versions (ubuntu-latest, beta)	1m 8s
cross-targets (x86_64-unknown-illumos)	1m 4s
timezones (macos-latest, ACST-9:30)	34s
alternative_targets (ubuntu-latest, aarch64-apple-ios)	12s
rust_versions (ubuntu-latest, nightly)	49s
timezones (macos-latest, EST4)	36s
alternative_targets (ubuntu-latest, aarch64-linux-android)	12s
timezones (macos-latest, UTC0)	32s
cross-tests (ubuntu-latest)	1m 40s
timezones (macos-latest, Asia/Katmandu)	34s
features_check (ubuntu-latest)	18s
test_wasi (ubuntu-latest, wasm32-wasi)	24s
timezones (windows-latest, ACST-9:30)	2m 44s
timezones (windows-latest, EST4)	1m 33s
test_wasm (ubuntu-latest)	39s
check-docs	22s
timezones (windows-latest, UTC0)	3m 0s
timezones (windows-latest, Asia/Katmandu)	2m 31s
	29m 16s

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