ci: add shellcheck workflow

.github/workflows/shellcheck.yml

@@ -0,0 +1,17 @@
+---
+name: shellcheck
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  shellcheck:
+    name: shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run ShellCheck
+        uses: ludeeus/action-shellcheck@master