Resolve "Broken master: uninitialized constant Events::RepositoryUpdatedEvent"

When run after ee/spec/features/dashboards/activity_spec.rb, this would fail to find the correct constant with:

NameError: uninitialized constant Events::RepositoryUpdatedEvent

I'm not sure why this was; we give Object.const_get a fully-qualified constant, and it should look that up first before attempting the default behaviour of finding constants in ancestor classes.

Alternatives:

• Object.const_get("::#{current_namespace}...") - didn't work.
• "::#{current_namespace}...".constantize - does work, but that is a bigger change as #constantize does much more work here.

Closes #9064 (closed).