BLD: pyproject.toml for Py38
Closes https://github.com/pandas-dev/pandas/issues/34666
Merging in a few hours if there's no objection. lets merge now! @MeeseeksDev backport to 1.0.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 1.0.x
$ git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
$ git cherry-pick -m1 08febd2b9f77fd8f943de92939788e8bc53ee2d2
```

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

```
$ git commit -am 'Backport PR #34667: BLD: pyproject.toml for Py38'
```

4. Push to a named branch :

```
git push YOURFORK 1.0.x:auto-backport-of-pr-34667-on-1.0.x
```

5. Create a PR against branch 1.0.x, I would have named this PR:

> "Backport PR #34667 on branch 1.0.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).
                