Drop Python 3.7 leftovers

[mdmintz]

Type of changes

• Documentation / docstrings
• Tests
• Other

Description

Some Python 3.7 leftovers remained when support for Python 3.7 was dropped in https://github.com/Textualize/rich/releases/tag/v13.9.0.

This completes the drop. Eg. PyPI still shows support for 3.7.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.25%. Comparing base (9c74f03) to head (0a549ce).
Report is 83 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3514   +/-   ##
=======================================
  Coverage   98.25%   98.25%           
=======================================
  Files          74       74           
  Lines        8072     8098   +26     
=======================================
+ Hits         7931     7957   +26     
  Misses        141      141           

Flag	Coverage Δ
unittests	98.25% <ø> (+<0.01%)	⬆️

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[willmcgugan]

Thanks