ci: various improvements to workflow

.github/workflows/shellcheck.yml

@@ -0,0 +1,18 @@
+name: Shell Check
+
+on:
+  pull_request:
+    paths:
+      - "**/*.sh"
+
+jobs:
+  shellcheck:
+    name: runner / shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: shellcheck
+        uses: reviewdog/action-shellcheck@v1.18.0
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          reporter: github-pr-review