Merge both action workflows into one file

[chrbeckm]

Checklist

• All included images are public domain images or their respective licenses are respected (e.g. attribution for CC-BY)
• Images are reduced to around 2000px at the long edge and in jpg format

[maxnoe]

Use push on main + pull_requests please.

It's important to build pull request as pull request builds and not as branch builds, as branch builds on the local branhc but pull request builds on the merged result