Update annotations from Python 3.8 support

As stated in #5283, there are some annotation updates now that Python 3.8 is the minimum supported version. These should be done for all modules.

Read issue #5283 first, since this issue says it defines the annotation updates required by the Python 3.8 minimum. Then inventory annotations across all beets modules and update the affected ones; done means the requested changes are applied consistently throughout the modules.

Written by the indexing model from the issue text.