Support isort 6

[cjwatson]

The breaking changes in isort 6 are just to remove support for Python 3.8 (see https://github.com/PyCQA/isort/releases), so there's no need for this project to treat it differently from isort 5.

[cjwatson]

I see the pre-commit failure, but it seems to be entirely due to running with the fact that the check now runs with poetry-core 2.0.1, rather than anything to do with my changes. Do you want me to include the results of running poetry lock anyway?

[cjwatson]

Hm, since pre-commit passed in #2290, I guess I have no choice. I've updated poetry.lock.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.76%. Comparing base (dd92cd0) to head (2bf0467).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #2289      +/-   ##
===========================================
- Coverage   100.00%   99.76%   -0.24%     
===========================================
  Files           38       38              
  Lines         4307     4307              
  Branches       994      994              
===========================================
- Hits          4307     4297      -10     
- Misses           0        6       +6     
- Partials         0        4       +4     

Flag	Coverage Δ
unittests	99.48% <ø> (-0.19%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #2289 will not alter performance

_{Comparing cjwatson:isort-6 (2bf0467) with main (dd92cd0)}

Summary

✅ 31 untouched benchmarks