Description

Followup to #34854, and inspired by WordPress/twentytwentytwo@395e093#r61847726.

The group and columns blocks both add a default padding when a background is applied. Using :where it already had pretty low specificity. But it can be lower still, and this PR does so. By wrapping both the block and the background class to the where selector, the specificity is now low enough that the 60px margin wins out in the following example, despite the default padding rule being after the 60px rule:

.has-background {
	padding: 60px;
}

:where(.wp-block-group.has-background) {
	padding: 10px;
}

How has this been tested?

Test group and columns blocks with and without a background applied. Verify no visual changes otherwise.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).