marked as major as the 2.264 behaviour looks really bad

I can't duplicate the problem you're describing with Jenkins 2.264 and a development build of the git plugin. I have no issue with the https://github.com/jenkinsci/git-plugin/pull/997 changes but am not seeing the problem that you're seeing when I use mvn hpi:run with the code from the master branch.

Is this specific to git plugin 4.3.0 as described in the heading? Git plugin 4.3.0 includes your changes for tables to divs in the main editing but does not include the tables to divs fixes in the git publisher. That needs git plugin 4.4.5.

On the master branch with a fresh work directory:

1. start with hpi:run and 2.265
2. create a free style job
3. try save

it won't work because the page is broken

promoted builds and multiple-scms changes in the PR I opened earlier will at least make the page work

Screenshot on 2.265 after applying https://github.com/jenkinsci/git-plugin/pull/997 and clicking the add repository button:

It’s based on building from source

My attempt to duplicate it was done by building from source as well.

Command I used:

$ git log -n 3 --graph --pretty=oneline --abbrev-commit
*   088b4f69 (HEAD -> master, upstream/master, origin/master, origin/HEAD, cache/master, bare/master) Merge pull request #997 from timja/make-plugin-testable-hpi-run
|\
| * f4ab92a3 Make plugin testable with tables to divs
|/
*   5399d0f5 Merge pull request #994 from MarkEWaite/improve-README
$ mvn -Djenkins.version=2.265 -DskipTests compile hpi:run

Happy to merge the proposed change since I wanted to eventually remove multiple-scms anyway, but still perplexed that I don't see the failures that you're seeing

Now with further attempts and more scrolling I'm able to see the issue that you're seeing. Sorry it took me so long to find it on the page.

Bisected it to JENKINS-64040, I reverted the respective commit in core and the issue is solved.

git revert bbc3580d4c5fe3766dc4a530902f8ea4e20c87a3