Layout Grid: Rerender is closing the inline Inserter

[WunderBart]

This was discovered after the recent Gutenberg v14.2.0 upgrade (p1664214321796799/1664214321.580149-slack-CBTN58FTJ). Fortunately, it shouldn't affect many users because it requires a ⚡ fast click on the + button right after selecting the columns count. Such a speed is not an issue for the testing framework, though (Playwright), so for now, we needed to manually pause the execution to make the test pass, as there's nothing else we can hook on to (like an "is-loading" class or attribute change).

I'm attaching a repro video so it's clear what the bug looks like:

file.mov

/cc @fullofcaffeine @worldomonation