Reset branch if the devel branch is based on Factory

This happens in packages that change their devel project over time. Then
the commit in the devel project no longer has the parent in the devel branch
but is based on factory

lib/git.py

@@ -184,6 +184,9 @@ class Git:
     def branch_head(self, branch):
         return self.repo.references["refs/heads/" + branch].target
 
+    def set_branch_head(self, branch, commit):
+        self.repo.references["refs/heads/" + branch].set_target(commit)
+
     def gc(self):
         logging.info(f"Garbage recollect and repackage {self.path}")
         subprocess.run(