[Tooltip] Fix placement regression

[oliviertassinari]

I have found this regression having a quick look at #25215.

To reproduce, you can:

• open https://next.material-ui.com/components/tooltips/#positioned-tooltips
• keyboard focus the bottom-start case, the tooltip should open
• scroll the page up until the tooltip swap its placement

Before

After

[mui-pr-bot]

Details of bundle changes

Generated by 🚫 dangerJS against 6611bc3

[oliviertassinari]

I can't think of any easy way to test this. It's the CSS that is wrong, which should require a visual regression. We have two options:

1. Only fix the regressions (as I did here)
2. Figure out how to write a test, have it non-flaky, and resilient to future changes.

Considering that I could already do 1. in about 10 minutes and that the regression stayed unnoticed for only 10 days, I think that the most efficient direction is to move in (1.). At least, we have a reproduction in the PR's description.