DEP: Minimum supported Python version 3.9

[snowman2]

• Closes DEP: Python 3.8 Support #1111

[codecov]

Codecov Report

Merging #1245 (582fe3f) into main (8109fc4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1245   +/-   ##
=======================================
  Coverage   96.34%   96.34%           
=======================================
  Files          20       20           
  Lines        1805     1805           
=======================================
  Hits         1739     1739           
  Misses         66       66           

Impacted Files	Coverage Δ
pyproj/__init__.py	89.47% <ø> (ø)

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[greglucas]

You can also remove some of the typing imports with the minimum being 3.9.

pyupgrade --py39-plus `find . -name "*.py" -type f`