style(rustup-init/sh): ignore shellcheck SC2086 false positives

Since we're really using `$_retry` for command building,
this is clearly an exception to the SC2086 rule,
as listed in https://www.shellcheck.net/wiki/SC2086.

rustup-init.sh

@@ -638,15 +638,18 @@ downloader() {
         get_ciphersuites_for_curl
         _ciphersuites="$RETVAL"
         if [ -n "$_ciphersuites" ]; then
+            # shellcheck disable=SC2086
             _err=$(curl $_retry --proto '=https' --tlsv1.2 --ciphers "$_ciphersuites" --silent --show-error --fail --location "$1" --output "$2" 2>&1)
             _status=$?
         else
             warn "Not enforcing strong cipher suites for TLS, this is potentially less secure"
             if ! check_help_for "$3" curl --proto --tlsv1.2; then
                 warn "Not enforcing TLS v1.2, this is potentially less secure"
+                # shellcheck disable=SC2086
                 _err=$(curl $_retry --silent --show-error --fail --location "$1" --output "$2" 2>&1)
                 _status=$?
             else
+                # shellcheck disable=SC2086
                 _err=$(curl $_retry --proto '=https' --tlsv1.2 --silent --show-error --fail --location "$1" --output "$2" 2>&1)
                 _status=$?
             fi