CI: remove usage of legacy NPY_PROMOTION_STATE
We no longer need this, see also discussion in https://github.com/pandas-dev/pandas/pull/60140.

And this fixes CI on main (tests are currently failing if you use numpy >= 2 with this env variable set)
CI is passing, except for the pyarrow nightly build, which seems to be using numpy 1.26 Looks like I added a `numpy < 2` pin in `ci/deps/actions-311-pyarrownightly.yaml` in https://github.com/pandas-dev/pandas/pull/59046. Maybe that can be removed now.

If that works, maybe we can also remove the `nomkl` install patch as well now. The Arrow nightly build seems a good one to use a later numpy version, but it might still be useful to test 1.26 somewhere? This is all passing, so going to merge this to get CI green again. 

But I still think we ideally get the tests passing for numpy 1.26 as well (at some point our min version might be that version and we will test with it anyway. But will open a separate follow-up PR for that) 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 2.3.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 4bbb3ce5d5a7e0f24dc2d8c1faf26c3b5d55670d
```

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

```
git commit -am 'Backport PR #60144: CI: remove usage of legacy NPY_PROMOTION_STATE'
```

4. Push to a named branch:

```
git push YOURFORK 2.3.x:auto-backport-of-pr-60144-on-2.3.x
```

5. Create a PR against branch 2.3.x, I would have named this PR:

> "Backport PR #60144 on branch 2.3.x (CI: remove usage of legacy NPY_PROMOTION_STATE)"

And apply the correct labels and milestones.

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

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 Manual backport -> https://github.com/pandas-dev/pandas/pull/60153