Add Shellcheck action

Signed-off-by: Dan Webb <dan.webb@damacus.io>

Author: damacus

.github/workflows/linting.yml

@@ -0,0 +1,15 @@
+---
+name: "Lint"
+
+"on":
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Run ShellCheck
+        uses: ludeeus/action-shellcheck@2.0.0