update-checkout: add type hints to confirm_tag_in_repo

Author: MaxDesiatov

utils/update_checkout/update_checkout/update_checkout.py

@@ -75,6 +75,7 @@ def check_parallel_results(results, op):
 
 
 def confirm_tag_in_repo(tag, repo_name):
+    # type: (str, str) -> str | None
     """Confirm that a given tag exists in a git repository. This function
     assumes that the repository is already a current working directory before
     it's called.
@@ -84,7 +85,8 @@ def confirm_tag_in_repo(tag, repo_name):
         repo_name (str): name the repository for the look up, used for logging
 
     Returns:
-        str: returns `tag` argument value or `None` if the tag doesn't exist.
+        str | None: returns `tag` argument value or `None` if the tag doesn't
+        exist.
     """
 
     tag_exists = shell.capture(['git', 'ls-remote', '--tags',