build: drop support for Python 3.7

[sisp]

I've dropped support for Python 3.7. Resolves #1251.

[codecov]

Codecov Report

Merging #1252 (fe6887c) into master (295d35a) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1252      +/-   ##
==========================================
+ Coverage   96.79%   96.85%   +0.06%     
==========================================
  Files          47       47              
  Lines        3930     3881      -49     
==========================================
- Hits         3804     3759      -45     
+ Misses        126      122       -4     

Flag	Coverage Δ
unittests	96.85% <100.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tests/test_dirty_local.py	100.00% <ø> (ø)
copier/main.py	95.79% <100.00%> (+0.13%)	⬆️
copier/subproject.py	97.36% <100.00%> (-0.20%)	⬇️
copier/template.py	96.24% <100.00%> (-0.07%)	⬇️
copier/tools.py	95.71% <100.00%> (+1.39%)	⬆️
copier/types.py	87.87% <100.00%> (-1.02%)	⬇️
copier/user_data.py	94.95% <100.00%> (+0.30%)	⬆️
copier/vcs.py	97.05% <100.00%> (-0.03%)	⬇️
tests/helpers.py	97.22% <100.00%> (-0.12%)	⬇️
tests/test_subdirectory.py	100.00% <100.00%> (ø)
... and 3 more

... and 2 files with indirect coverage changes

[sisp]

It seems thatshutil.rmtree doesn't only have this issue under Python <3.8 on Windows. See the Windows CI checks when I had this handler removed: https://github.com/copier-org/copier/actions/runs/5573531416

It seems okay to remove the custom TemporaryDirectory class though. I hope that's actually correct and not just uncovered by tests.

[pawamoy]

Is the handle_remove_readonly utility still used somewhere else in the code?

[sisp]

No, only in template.Template._cleanup.

[sisp]

I think this PR is ready for a review now.

I'm not sure why there are 3 build (<OS>-latest, 3.7) jobs, they shouldn't exist because I removed "3.7" from the CI matrix. 🤔

[yajo]

That was due to repo settings. Fixed now.

[sisp]

Checks are passing now. 🎉

[sisp]

@yajo Haha, looks like I'm still struggling with the commit change types. 😆 I was actually wondering whether build: was a bad choice because it wouldn't appear in the changelog.