BUG: raise when sort_index with ascending=None
- [ ] closes #39434
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

Added validation of ``ascending`` for ``sort_index`` methods.
Proposed a solution to raise ``ValueError`` when either of the elements of ``ascending`` turned out to be ``None``.
can you merge master and fixup to comments. ok looks fine. can you add a whtasnew note for 1.2.3 in regression section. merge master and ping on green. thanks @ivanovmg  @meeseeksdev backport 1.2.x 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 1.2.x
$ git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
$ git cherry-pick -m1 78371ccbd8744326e8535ac8bb9a661b073dfd88
```

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

```
$ git commit -am 'Backport PR #39451: BUG: raise when sort_index with ascending=None'
```

4. Push to a named branch :

```
git push YOURFORK 1.2.x:auto-backport-of-pr-39451-on-1.2.x
```

5. Create a PR against branch 1.2.x, I would have named this PR:

> "Backport PR #39451 on branch 1.2.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](https://github.com/MeeseeksBox/MeeseeksDev).
                