ci(tests): add optional workflow for generating grammars

run on PR by adding label `ci:generate` or manually

.github/workflows/test-generate.yml

@@ -0,0 +1,20 @@
+name: Generate from grammar
+
+on:
+  pull_request:
+    types: [unlabeled, labeled, opened, synchronize, reopened]
+    branches:
+      - "main"
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  check_compilation:
+    name: Build
+    if: contains(github.event.pull_request.labels.*.name, 'ci:generate') || github.event_name == 'workflow_dispatch'
+    uses: ./.github/workflows/test-core.yml
+    with:
+      type: "generate"