[20215] Update PR checklist template. Backports and Description (backport #4215)

[mergify]

This is an automatic backport of pull request #4215 done by Mergify.
Cherry-pick of dbbb465 has failed:

On branch mergify/bp/2.11.x/pr-4215
Your branch is up to date with 'origin/2.11.x'.

You are currently cherry-picking commit dbbb46532.
  (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)

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

no changes added to commit (use "git add" and/or "git commit -a")

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

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More conditions and actions can be found in the documentation.

You can also trigger Mergify actions by commenting on this pull request:

• @Mergifyio refresh will re-evaluate the rules
• @Mergifyio rebase will rebase this PR on its base branch
• @Mergifyio update will merge the base branch into this PR
• @Mergifyio backport <destination> will backport this PR on <destination> branch

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