Speed up github workflow by enabling numba jit and test coverage includes only xcube package

[konstntokas]

1. Closes #946 unit tests take ~5min which is comparable to local machine (https://github.com/xcube-dev/xcube/actions/runs/9095416416/job/24998584637)
2. Text coverage includes only the xcube package. Note that the text coverage decreases, since the the test folder is not considered anymore in the test coverage report.
3. github actions are updated.

Checklist:

• [ ] ~Add unit tests and/or doctests in docstrings~
• [ ] ~Add docstrings and API docs for any new/modified user-facing classes and functions~
• [ ] ~New/modified features documented in docs/source/*~
• [x] Changes documented in CHANGES.md
• [x] GitHub CI passes
• [x] AppVeyor CI passes
• [ ] Test coverage remains or increases (target 100%)

[konstntokas]

Should we remove one of the platforms in appveyor to double the speed, as @pont-us suggested? (https://ci.appveyor.com/project/bcdev/xcube/builds/49819045)

[pont-us]

Should we remove one of the platforms in appveyor to double the speed, as @pont-us suggested? (https://ci.appveyor.com/project/bcdev/xcube/builds/49819045)

I think this would make sense, since with the speed-up GHA should now be faster than AppVeyor on two platforms. In that case it probably makes the most sense to disable Ubuntu2204 and keep macos, since we're using Ubuntu on GHA. I'd just comment out the Ubuntu2204 item in the "image" section and keep the rest of the configuration in place in case we ever want to re-enable it.