Add shellcheck lint GH actions job

.github/workflows/test.yml

@@ -26,3 +26,14 @@ jobs:
             for f in $(find . -name '*.jsonnet' -print); do
               jsonnetfmt --pad-arrays --test -- $f
             done
+
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: reviewdog/action-shellcheck@v1
+        with:
+          reporter: github-pr-review
+          pattern: |
+            *.sh
+            step-*