Geo: Wiki HEAD ref not replicated

Problem

A customer noticed the HEAD ref was missing in some wiki repositories on a Geo secondary site.

When the HEAD ref on a Geo secondary site does not match the HEAD ref on the primary, it's not a data loss risk. But we expect wiki verification to fail in that case.

Geo did not need to replicate the wiki repository HEAD ref before. Something changed recently and it seems we now need to that.

Similar to #334586 (closed).

Proposal

It may be as simple as moving def update_root_ref up to the superclass RepositoryBaseSyncService and calling it in WikiSyncService too.

We should pick the fix into 14.1 (and 14.2 if it misses).