GitLab

Backport #20893

In the compare endpoint the git fetch is restricted to a certain branch however,
this does not completely prevent tag acquisition/pollution as git fetch will collect
any tags on that branch.

This causes pollution of the tag namespace and could cause confusion by users.

This PR adds `--no-tags` to the `git fetch` call.
Signed-off-by: Andrew Thornton <art27@cantab.net>
Signed-off-by: Andrew Thornton <art27@cantab.net>