Update `release-docs` to work with patch releases

[sgagniere]

Release Notes

Breaking Changes

• PLACEHOLDER

New Features

• PLACEHOLDER

Bug Fixes

• PLACEHOLDER

Checklist

• [x] Leave this box unchecked if features are not yet available in production

What

For patch versions, release-docs was still attempting to push directly to protected branches.

Instead of attempting to push to the -post branch, this PR just opens a PR to pull the new command-reference and release-notes.rst from the .x branch into the -post branch.

I didn't merge .x into -post to avoid picking up incorrect changes to settings.sh and conf.py. These files will be updated in the -post branch anyway by release-docs-staging

References

Test & Review