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/close-invalid-bot.yaml

@@ -1,10 +1,10 @@
-# Close issues marked as invalid
-name: "Close issues marked as invalid"
+# Close issues marked as not_on_github
+name: "Close issues marked as not_on_github"
 on:
   schedule:
     - cron: '0 */6 * * *'
 jobs:
-  close_invalid:
+  close_issues:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/github-script@v3
@@ -14,7 +14,7 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               state: 'open',
-              labels: 'invalid',
+              labels: 'not_on_github',
               per_page: 100,
               page: 1
             });