Setup GitHub actions cmd check and code coverage

[SunnyTseng]

• Added the CMD check and the code coverage into the GitHub actions workflow
• The failed tests were fixed by running reticulate::install_python(version = "3.11") and birdnetR::install_birdnet(). All tests were successfully run locally.
• Made sure there is a valid Python installation on the runner, and that reticulate knows to use it in GitHub Actions (instructions)
• Try the Pull Request to initiate the Github Action and see how the tests go.

[kahst]

Thanks @SunnyTseng , I'll let Felix do the review and merge, he's on vacation though, and it might take a while before we can proceed.

[SunnyTseng]

Thanks @kahst ! 🚀 There are still some error messages from the Github Action (R CMD check) that need to be addressed before merge. The devtools::check() can run without errors on my local computer, so I guess it's about the environment set up in the Github Action.

[fegue]

Hey Sunny, I am trying to get the custom model into the package as soon as possible. If thats done, I am going to take a look at this problem.
Thank you for your participation!

[fegue]

Yeah! Most checks work now :)

[fegue]

Actually, all checks work. I just have a few comments / questions in the code. See the review

[fegue]

Thanks for the great work. This is really helpful

[SunnyTseng]

Woohoo!! All checks have passed! I think this PR is ready to be merged! 🚀

[fegue]

Great! You can merge it when you are ready