Run pyupgrade --py38-plus on source

[jwodder]

Plus some manual corrections of the results.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (b6717fb) 89.05% compared to head (a59ab3b) 89.05%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1350   +/-   ##
=======================================
  Coverage   89.05%   89.05%           
=======================================
  Files          75       75           
  Lines       10284    10284           
=======================================
  Hits         9158     9158           
  Misses       1126     1126           

Flag	Coverage Δ
unittests	89.05% <88.00%> (ø)

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Files	Coverage Δ
dandi/cli/command.py	46.91% <ø> (ø)
dandi/cli/formatter.py	94.11% <100.00%> (ø)
dandi/dandiapi.py	87.43% <100.00%> (ø)
dandi/download.py	88.46% <100.00%> (ø)
dandi/due.py	48.00% <100.00%> (ø)
dandi/organize.py	85.26% <100.00%> (ø)
dandi/support/pyout.py	85.07% <100.00%> (ø)
dandi/tests/fixtures.py	97.57% <ø> (ø)
dandi/tests/skip.py	89.06% <100.00%> (ø)
dandi/tests/test_keyring.py	100.00% <ø> (ø)
... and 4 more

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[github-actions]

🚀 PR was released in 0.58.1 🚀