sync-pr-commit-title messing up PR title

[FloEdelmann]

I squashed and merged this PR without changing the commit title. Afterwards, the PR title was messed up:

The commit title is fine:

Unfortunately, I cannot remember if the feature suggested the title change before merging.

[FloEdelmann]

It didn't happen for a similar PR: OpenLightingProject/open-fixture-library#1642

[FloEdelmann]

It happened again:

• Fix some links OpenLightingProject/open-fixture-library#1645
• Fix typo Date.new() → Date.now() OpenLightingProject/open-fixture-library#1646

Now I am sure that it didn't suggest (or rather warn in this case 😅) to change the title before merging.

[FloEdelmann]

New insights 💡

It's caused by GitHub's new (beta) auto-merge feature:

When a PR can't be merged immediately due to failing tests or missing reviews, the .is-squashing element now contains two similar forms: One for overriding branch restrictions as an admin, and a new one to enable auto-merge once all restrictions are met.

In both, there is a commit message input with id merge_title_field.

The code in sync-pr-commit-title expects this input to exist only once and thus only operates on the first one, regardless whether it is hidden (which was the case for aforementioned PRs) or not.