ci: add optional codegen step to CI

.github/workflows/ash-ci.yml

@@ -8,6 +8,9 @@ on:
       spark-formatter:
         type: boolean
         default: true
+      codegen:
+        type: boolean
+        default: false
       spark-cheat-sheets:
         type: boolean
         default: true
@@ -147,6 +150,17 @@ jobs:
         if: ${{inputs.spark-formatter}}
         with:
           mix-env: test
+  codegen:
+    name: mix ash.codegen --check
+    runs-on: ubuntu-latest
+    needs: build-test
+    if: ${{inputs.codegen}}
+    steps:
+      - uses: actions/checkout@v3
+      - uses: team-alembic/staple-actions/actions/mix-task@main
+        with:
+          mix-env: test
+          task: ash.codegen --check
   unused-deps:
     name: mix deps.unlock --check-unused
     runs-on: ubuntu-latest