Replace _pytest imports with modern pytest imports

[jwodder]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9335182) 89.04% compared to head (bcd1d93) 89.03%.
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1347      +/-   ##
==========================================
- Coverage   89.04%   89.03%   -0.02%     
==========================================
  Files          76       76              
  Lines       10243    10240       -3     
==========================================
- Hits         9121     9117       -4     
- Misses       1122     1123       +1     

Flag	Coverage Δ
unittests	89.03% <100.00%> (-0.02%)	⬇️

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

Files	Coverage Δ
dandi/conftest.py	100.00% <100.00%> (ø)
dandi/tests/fixtures.py	97.55% <ø> (-0.01%)	⬇️

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[yarikoptic]

let's merge when CI finishes up

[jwodder]

@yarikoptic CI is currently quiet.

[github-actions]

🚀 PR was released in 0.58.1 🚀