Add ShellCheck GitHub workflow

.github/workflows/shell.yml

@@ -0,0 +1,22 @@
+name: ShellCheck
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  shellcheck:
+    name: ShellCheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run ShellCheck for shell scripts
+        uses: ludeeus/action-shellcheck@master
+        with:
+          severity: style
+          scandir: .
+          format: gcc
+          version: stable