Followup to PR #55657

[peterguy]

Implemented suggestions to remove debug code, add test and fix typo

Test plan

gitdomain test will include a test of the newly-allowed git commit arguments

[eseliger]

Thank you!

[sourcegraph-bot]

Codenotify: Notifying subscribers in CODENOTIFY files for diff 632927a...1497747.

Notify	File(s)
@indradhanush	cmd/gitserver/server/patch.go
@sashaostrikov	cmd/gitserver/server/patch.go

[github-actions]

The backport to 5.1 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-5.1 5.1
# Navigate to the new working tree
cd .worktrees/backport-5.1
# Create a new branch
git switch --create backport-55682-to-5.1
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 3a9f5030d6480df2bf7c50ef3bfd42d6aca34a52
# Push it to GitHub
git push --set-upstream origin backport-55682-to-5.1
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-5.1

Then, create a pull request where the base branch is 5.1 and the compare/head branch is backport-55682-to-5.1.