REGR: inplace Series op not actually operating inplace

[jbrockmendel]

• closes REGR: inplace arithmetic operation on Series no longer updating parent DataFrame #36373
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

alternative to #37497, ensures that Series inplace ops are actually inplace whenever possible. The whatsnew is copied verbatim from #37497, the new test is copied with an additional assertion about series._values

[jorisvandenbossche]

Thanks!

[jorisvandenbossche]

@meeseeksdev backport to 1.1.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout 1.1.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 d8c8cbb90544b77e5da1daa7274eba7bef3257b9

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #37508: REGR: inplace Series op not actually operating inplace'

4. Push to a named branch :

git push YOURFORK 1.1.x:auto-backport-of-pr-37508-on-1.1.x

5. Create a PR against branch 1.1.x, I would have named this PR:

"Backport PR #37508 on branch 1.1.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.