feat: add ability to run commitlint on events that are not pull requests

For any event that is not of type `pull_request`, we consider there will be a `GITHBU_SHA` defined and run lint against only this specific commit
sha.
This supports not only events of type `pull` but also other events that provide us a `GITHBU_SHA`, like `check_suite`.

.github/workflows/test.yml

@@ -0,0 +1,11 @@
+name: Test
+on: [push]
+
+jobs:
+  commitlint:
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@v1
+      - uses: ./