git-update: Update submodules too

More correct than not doing it, and prevents careless people from
mistakenly pushing changes to submodules.

git-update

@@ -49,6 +49,7 @@ def update_repo(repo_name, repo_dir, revision, no_interaction, recurse_i=0):
             git("checkout", revision, repository_path=repo_dir)
         else:
             git("pull", "--rebase", repository_path=repo_dir)
+        git("submodule", "update", repository_path=repo_dir)
     except Exception as e:
         out = getattr(e, "output", b"").decode()
         if not no_interaction: