add differential shellcheck action

.github/workflows/differential-shellcheck.yml

@@ -0,0 +1,37 @@
+name: Differential ShellCheck
+on:
+  push:
+    branches:
+    - main
+    - rel-*
+  pull_request:
+    branches:
+    - main
+    - rel-*
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    permissions:
+      # required for all workflows
+      security-events: write
+
+      # only required for workflows in private repositories
+      actions: read
+      contents: read
+
+    steps:
+      - name: Repository checkout
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # [email protected]
+        with:
+          fetch-depth: 0
+
+      - id: ShellCheck
+        name: Differential ShellCheck
+        uses: redhat-plumbers-in-action/differential-shellcheck@91e2582e40236f831458392d905578d680baa138 # pin@aa647ec4466543e8555c2c3b648124a9813cee44
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}