[8.13](backport #3916) Delete serverless directory on backport PRs

[mergify]

Simplified version of #3889 that doesn't work for some reason. Introduces conflicts. works after @colleenmcginnis fixed it.

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This is an automatic backport of pull request #3916 done by Mergify.

[mergify]

Cherry-pick of 4a57e39 has failed:

On branch mergify/bp/8.13/pr-3916
Your branch is up to date with 'origin/8.13'.

You are currently cherry-picking commit 4a57e394.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   .github/workflows/delete-serverless-dir-on-backports.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   README.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally