[CI] Github action shall moinitor main branch

[kimkulling]

Describe the bug The current CI actions are just monitoring the wrong branch: master. Instead fo this main shall be monitored.

To Reproduce Steps to reproduce the behavior:

1. Create a branch
2. Wait for CI ok
3. Nothing happens

Expected behavior CI shall llok for PRs to main.

Screenshots NA

Desktop (please complete the following information):

• OS: All

Additional context NA