.github/request-reviews.yml: Update PR reviewer exclusion

Updates logic to:

- Not request reviews from reviewers that have already left a review
  on the PR. Previously, the reviewers review (e.g. approval) would
  remain on the PR, but they would be notified on each change to the
  PR. This approach follows the expected notification process for
  requesting reviews which is one time. Maintainers and reviewers can
  set up their own notifications for more granular updates on PR
  activity separately.

- Add the collaborator reviewers if a reviewer(s) is found to not be
  a collaborator. This is an improvement to today's behavior which is
  to not add any reviewers if a single reviewer is not a collaborator
  of the repo.

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

.github/scripts/GitHub.py

@@ -202,12 +202,20 @@ def add_reviewers_to_pr(
 
     pr_author = pr.user.login.strip()
 
-    while pr_author in user_names:
-        user_names.remove(pr_author)
+    current_pr_requested_reviewers = [
+        r.login.strip() for r in pr.get_review_requests()[0]
+    ]
+    current_pr_reviewed_reviewers = [r.user.login.strip() for r in pr.get_reviews()]
+    current_pr_reviewers = list(
+        set(current_pr_requested_reviewers + current_pr_reviewed_reviewers)
+    )
 
     repo_collaborators = [c.login.strip() for c in repo_gh.get_collaborators()]
     non_collaborators = [u for u in user_names if u 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]
+
     if non_collaborators:
         print(
             f"::error title=User is not a Collaborator!::{', '.join(non_collaborators)}"
@@ -225,6 +233,12 @@ def add_reviewers_to_pr(
             f"Users requested:\n{', '.join(user_names)}",
         )
 
-    pr.create_review_request(reviewers=user_names)
+    # Add any new reviewers to the PR if needed.
+    if new_pr_reviewers:
+        print(
+            f"::debug title=Adding New PR Reviewers::" f"{', '.join(new_pr_reviewers)}"
+        )
 
-    return user_names
+        pr.create_review_request(reviewers=new_pr_reviewers)
+
+    return new_pr_reviewers