workflows: Rename the "invalid" label to "not_on_github"

Use a more appropriate label name.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

.github/workflows/invalid-label-bot.yaml

@@ -1,5 +1,5 @@
-# Add a comment to github issues marked with the invalid label
-name: "Add comment to issues marked invalid"
+# Add a comment to github issues marked with the not_on_github label
+name: "Add comment to issues marked not_on_github"
 on:
   issues:
       types: [labeled]
@@ -11,7 +11,7 @@ jobs:
         with:
           github-token: ${{secrets.GITHUB_TOKEN}}
           script: |
-            if (context.payload.label.name != "invalid")
+            if (context.payload.label.name != "not_on_github")
               return;
             msg = "It looks like this ticket is a request for help"
                 + " (or similar)."