namespace consistency for test_dtype.py

[reshamas]

• [x ] references Fix cases of inconsistent namespacing in tests #37838
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[MarcoGorelli]

Can you drop the first commit?

So

git fetch --all --prune
git rebase -i upstream/master

then, in the interactive window, change the first pick to drop. Then (you may need to run this one twice)

pre-commit run --files pandas/tests/arithmetic/test_interval.py

Then,

git add pandas/tests/arithmetic/test_interval.py
git commit -m "fixup"  # or whatever message you like
git push origin namespace -f

Let me know if anything trips you up here

[MarcoGorelli]

can you revert this change? Only pd.Interval needed changing, not pd.IntervalDtype

[MarcoGorelli]

looks good now, thanks!