Drop python 3.9 and run pyupgrade

[semohr]

Drops support for python 3.9 and runs pyupgrade on the whole codebase.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.26%. Comparing base (4262c46) to head (24d1678).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #94   +/-   ##
=======================================
  Coverage   93.26%   93.26%           
=======================================
  Files          16       16           
  Lines         817      817           
  Branches      118      118           
=======================================
  Hits          762      762           
  Misses         35       35           
  Partials       20       20           

Files with missing lines	Coverage Δ
mediafile/fields.py	93.16% <100.00%> (ø)
mediafile/storage/afs.py	97.67% <100.00%> (ø)
mediafile/storage/ape.py	100.00% <100.00%> (ø)
mediafile/storage/base.py	90.69% <100.00%> (ø)
mediafile/storage/flac.py	100.00% <100.00%> (ø)
mediafile/storage/mp3.py	92.69% <100.00%> (ø)
mediafile/storage/mp4.py	100.00% <100.00%> (ø)
mediafile/storage/vorbis.py	89.18% <100.00%> (ø)
mediafile/utils/image.py	90.62% <100.00%> (ø)

[JOJ0]

LGTM