General: Add `svn:mergeinfo` missed in [48733].

Finishes merging [48729-48730] to the 5.5 branch.
See #50416.
Built from https://develop.svn.wordpress.org/branches/5.5@48740


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48502 1a063a9b-81f0-0310-95a4-ce76da25c4cd