Add shellcheck CI step

.github/workflows/shellcheck.yml

@@ -0,0 +1,19 @@
+name: Shellcheck
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install shellcheck
+        run: sudo apt update && sudo apt install --assume-yes shellcheck
+
+      - name: Run shellcheck
+        run: find . -name \*.sh | xargs shellcheck --severity=warning