.github/request-reviews.yml: Only post non-collab message once

Enhances the flow that adds a comment on a PR if a non-collaborator
is in the reviewer list by checking if a comment was previously left
on the PR. If it was for the same set of non-collaborators, another
comment is not created. If a new non-collaborator is discovered, the
message will be left identifying that new user account.

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

.github/scripts/GitHub.py

@@ -221,6 +221,16 @@ def add_reviewers_to_pr(
             f"::error title=User is not a Collaborator!::{', '.join(non_collaborators)}"
             )
 
+        for comment in pr.get_issue_comments():
+            # If a comment has already been made for these non-collaborators,
+            # do not make another comment.
+            if (
+                comment.user.login == "github-actions[bot]"
+                and "WARNING: Cannot add some reviewers" in comment.body
+                and all(u in comment.body for u in non_collaborators)
+            ):
+                break
+        else:
             repo_admins = [
                 a.login for a in repo_gh.get_collaborators(permission="admin")
             ]