Is your feature request related to a problem? Please describe.
Currently the default styles of buttons blocks results in its
containing button blocks being aligned horizontally.
This can be annoying if existing, singular button blocks (from a time where Gutenberg hadn't used a wrapper buttons block when a button block is inserted) are transformed to be wrapped by a buttons block, because singular button blocks on each line would suddenly put on a single line in the containing buttons block.

It would therefore make sense to either add a "Vertical" core block style for the buttons block or style the buttons block default styles to vertically aligned button blocks right away.

Describe the solution you'd like
"Vertical" block style for buttons block -or-
Default blocks styles align its containing button blocks vertically, one on each line.

Describe alternatives you've considered
The alternative would be to add such a "vertical" buttons block style by plugin/theme or re-styling the default buttons block style by plugin/theme, or adding some inline styles. This can be a hassle for users that migrate singular button blocks to wrapped button blocks in buttons blocks.