Ensure the repo project is never fetched with partial depth

If the repo project is synced with partial depth, then the tags
won't be fetched and users will be told the newest sha1 in the
stable branch isn't signed.

Change-Id: I107df97b4836b928c76aa33a700fa35d1705ae09

project.py

@@ -1749,6 +1749,9 @@ class Project(object):
         depth = self.clone_depth
       else:
         depth = self.manifest.manifestProject.config.GetString('repo.depth')
+      # The repo project should never be synced with partial depth
+      if self.relpath == '.repo/repo':
+        depth = None
 
     if depth:
       current_branch_only = True