CI post-release.yml also runs during push to master

[viferga]

I have tried to improve this CI to run only when a release is made, but I couldn't. I am leaving the issue until we find a way:

55eb148

I am thinking to unify them or search for an alternative like in here:

https://stackoverflow.com/questions/65324440/github-actions-using-workflow-run-based-on-new-tags