[pre-commit] Move codespell-log back to commit-msg stage

Commit 7acd390ffd9 ("[pre-commit] Move codespell-log to post-commit") moved
the codespell-log hook from the commit-msg to the post-commit stage.

This was deemed to make git rebase too slow [1], so move it back to the
commit-msg stage.  Don't do this using a full revert, to keep unrelated
improvements from that commit.

Since we use codespell-log to produce warnings rather than errors, running the
hook at the commit-msg stage requires us to ignore codespell exit status, and
set verbose=true.

[1] https://sourceware.org/pipermail/gdb-patches/2025-December/223533.html