don't post messages PRS with stale label

fixes #7

main.py

@@ -170,6 +170,8 @@ def update_pr_messages(self):
             if len(self.libs[lib_name]) <= 1:
                 continue
             for issue_number in self.libs[lib_name]:
+                if any(label["name"] == "stale" for label in self.prs[issue_number]["labels"]):
+                    print("skipping %s message because PR is stale" % issue_number) 
                 if dateutil.parser.isoparse(self.prs[issue_number]["updated_at"]) < datetime.now(timezone.utc) - timedelta(days=15):
                     print("skipping %s message because PR has not been updated since %s" % (issue_number, self.prs[issue_number]["updated_at"]))
                     continue