Triggering more tests in PRs

[Akuli]

In #1195 we wanted to run armv6 tests, which don't run by default, because they are really really slow. It would have been nice to add a label, similar to the existing run macos tests label, that causes those tests to run.

I was going to suggest adding labels like run tests on raspios armv6 or run tests on alpine x86, but it might be easier to just add a run tests on all platforms label. I think we should still keep the run macos tests (perhaps rename to run tests on macos label for clarity/consistency), so that if you change something MacOS specific, you don't need to wait 1h30min for the ridiculous Raspberry Pi OS armv6 tests.

Todo list:

• create run tests on all platforms label
• run tests on all platforms label triggers all VM tests
• run tests on all platforms label triggers MacOS tests
• rename run macos tests to run tests on macos

[Akuli]

The run tests on all platforms should probably also trigger valgrinding.

Edit And there should probably be a separate run tests with valgrind label too, so that you don't need to wait for that 1h30min run if you just want to valgrind...

Edit 2: I don't think this is needed right now. It's easy enough to valgrind locally. Might add later.