Invalid core.commentChar breaks rebase #2500

I can't rebase anymore since v2026.14.

The log:

$ git -c core.commentChar=± rebase --autostash ...

error: core.commentChar should only be one ASCII character
fatal: unable to parse 'core.commentchar' from command-line config

This commit seems to be the culprit: e92810e

Git requires core.commentChar to be a single ASCII character (one byte). UTF-8 represents ± as two bytes:

$ echo -n "±" | xxd

00000000: c2b1

I'm using Ubuntu 24.04.4 and git 2.43.0.