Describe the bug
When opening the menu for a block close to the bottom of the viewport the positioning is inconsistent.
To Reproduce
Reproduced in https://www.blocknotejs.org/examples/basic/minimal
Position content and editor so the empty block is close to the bottom of the viewport (but not too close)

Click on a plus once, the menu is positioned above the empty block:

Click on same plus second time, the menu is positioned below and very small:

Misc