Split push vs. pull_request lint tooling (#426)

.github/workflows/reviewdog.yml

@@ -0,0 +1,16 @@
+name: Reviewdog
+on: [pull_request]
+jobs:
+  vint:
+    strategy:
+      fail-fast: false
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Lint Vimscript in PR changes
+      uses: reviewdog/action-vint@v1
+      with:
+        github_token: ${{ secrets.github_token }}
+        reporter: github-pr-review
+        level: info