How to run Workflow only if it is a tag from merge request into main branch?

Hello, I’m trying to figure out how to accomplish this:

  1. Have a release branch: git checkout -b release-v0.1.0
  2. Commit some changelog: (automated script the append
  3. The automated script will also tag the commit: echo "release v0.1.0" | git tag -a -F- v0.1.0
  4. Open a Pull Request for release
  5. Only run the workflow if and only if the PR is merged into the main branch

I can’t seem to figure it out with Github Actions. This was very useful with BitBucket and TeamCity…