.github: Compare collaborator GitHub ID's in single case

Since case of a GitHub user name may by specified differently in the
`Maintainers.txt` file versus what is actually returned by the GitHub
API (actual case), convert both to lowercase for comparison.

Other GitHub user name inputs are directly from APIs and maintain
consistent casing.

Signed-off-by: Michael Kubacki <[email protected]>

Author: makubacki

.github/scripts/GitHub.py

@@ -228,8 +228,8 @@ def add_reviewers_to_pr(
     )
 
     # A user can only be added if they are a collaborator of the repository.
-    repo_collaborators = [c.login.strip() for c in repo_gh.get_collaborators() if c]
-    non_collaborators = [u for u in user_names if u not in repo_collaborators]
+    repo_collaborators = [c.login.strip().lower() for c in repo_gh.get_collaborators() if c]
+    non_collaborators = [u for u in user_names if u.lower() not in repo_collaborators]
 
     excluded_pr_reviewers = [pr_author] + current_pr_reviewers + non_collaborators
     new_pr_reviewers = [u for u in user_names if u not in excluded_pr_reviewers]