Allow 'region' key to be a string for placeBlockInDefaultTheme and placeBlockInAdminTheme config actions

I propose a slightly different variant: let's just allow the region to be a string, instead of an array. If it's a string, it's passed through to the EntityCreate plugin unaltered.

OK, this works to use a string unmodified if that has been set for the region.

Just a title update

nod_ → closed merge request !8897

Committed 5acde36 and pushed to 11.x. Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.