ci: Allow other workflows to trigger linting (#2220)

This should resolve the issue of the lint workflow not being triggered by PRs opened via another workflow (`contributors.yml`).

This workflow will be triggered after the dependent workflow completes (regardless of status).

.github/workflows/linting.yml

@@ -6,6 +6,12 @@ on:
   push:
     branches:
       - master
+  # These workflows when done will trigger this workflow too:
+  workflow_run:
+    workflows: ['Update contributors']
+    types:
+      - completed
+
 jobs:
   lint:
     runs-on: ubuntu-20.04