Summary

Extended regular expressions (enabled via flag -E) don't support non-capturing groups under POSIX. Get rid of them as they don't add any value since we don't handle the captured groups in the first place.

The warning is:

$ ./scripts/sync-version
grep: warning: ? at start of expression
grep: warning: ? at start of expression
grep: warning: ? at start of expression
grep: warning: ? at start of expression
grep: warning: ? at start of expression
grep: warning: ? at start of expression

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.