Don't show group block's placeholder when there is only one variation available

[costasovo]

What problem does this address?

When someone limits a group block's variations so that there is only one left. The block still shows a placeholder and asks a user to pick a variation. The placeholder step could be skipped and the only variation could be used directly.

The real-world use-case is the email editor, where we are not able to support Flex or Grid because these are not supported by email clients.

What is your proposed solution?

The block could select the single variation automatically and skip the placeholder step.

There is a PR that adds this behavior #61871.