Do not fetch VCS deps when reference didn't change (#6131)

* Do not fetch VCS deps when reference didn't change
* test(solver): test that solver does not update the resolved reference of a locked vcs package if not requested
* test(solver): test that vcs package with locked ref is not refetched

Co-authored-by: Randy Döring <30527984+radoering@users.noreply.github.com>