[improve][CI] Support GitHub Actions approval solution on maintenance branches

[lhotari]

Motivation

The GitHub Actions approval solution is also useful for maintenance branches to cut unnecessary builds. branch-2.11 contains a similar workflow as master branch and it will also be useful to port the approval to other maintenance branches as a way to prevent unnecessary builds.

Modifications

Remove the hard coding of master branch in the script which generates the link for opening a PR in your fork.

Documentation

• [ ] doc-required (Your PR needs to update docs and you will update later)

• [x] doc-not-needed (Please explain why)

• [ ] doc (Your PR contains doc changes)

• [ ] doc-complete (Docs have been already added)

Matching PR in forked repository

PR in forked repository: https://github.com/lhotari/pulsar/pull/90