If a repository return no commitstatus, then still cache it but not query it from...

If a repository return no commitstatus, then still cache it but not query it from database (#30700)

The previous repository default branch commit status cache will only
store if the commit status has value. So the repository which have no
any commit status will always be fetched from database.

This PR will store the empty state of commit status of a repository into
cache because the cache will be updated once there is a commit status
stored.