CI: Fix branch syntax, bump action and python versions to current, fix indent

[C0rn3j]

branch is not valid, branches is (maybe it was valid in the past?).

[tehkillerbee]

LGTM although I have not looked further into the CI/CD configuration, as I do not currently have the necessary permissions. We need to move the project to an org. first before this is possible so I will wait a bit with merging this one.

[nyabinary]

LGTM although I have not looked further into the CI/CD configuration, as I do not currently have the necessary permissions. We need to move the project to an org. first before this is possible so I will wait a bit with merging this one.

When is the project moving to an org?

[tehkillerbee]

LGTM although I have not looked further into the CI/CD configuration, as I do not currently have the necessary permissions. We need to move the project to an org. first before this is possible so I will wait a bit with merging this one.

When is the project moving to an org?

It has just been moved today. I will look into setting up CI/CD ASAP.