GHA: add a sanity shellcheck (#2)

Perform some sanity checks on shell scripts.

.github/workflows/sanity.yml

@@ -0,0 +1,36 @@
+name: "Sanity checks"
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  shellcheck:
+    name: 'shellcheck'
+    strategy:
+      fail-fast: false
+      # Run on Linux
+      matrix:
+        os: [ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: 'Checkout repository'
+        uses: actions/[email protected]
+      - name: 'Install shellcheck on Ubuntu'
+        run: |
+            sudo apt update
+            sudo apt install shellcheck -y
+
+      - name: Run shellcheck
+        run: |
+            set -euxo pipefail
+            cd ${{ github.workspace }}/
+            shellcheck --version
+            for f in $(find . -path ./.git -prune -o -type f -print); do
+            if file "$f" | grep "shell script" &>/dev/null; then
+                shellcheck "$f"
+            fi
+            done