feat: add build tests for non-PRs that rely on pinned v12

Author: BenHenning

.github/workflows/build.yml

@@ -12,7 +12,55 @@ permissions:
   contents: read
 
 jobs:
+  build_tip_of_tree_v12:
+    name: Build test (against tip-of-tree core v12)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout experimentation plugin
+        uses: actions/checkout@v4
+        with:
+          path: main
+
+      - name: Checkout core Blockly
+        uses: actions/checkout@v4
+        with:
+          repository: 'google/blockly'
+          ref: 'rc/v12.0.0'
+          path: core-blockly
+
+      - name: Use Node.js 20.x
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20.x
+
+      - name: NPM install
+        run: |
+          cd main
+          npm install
+          cd ..
+          cd core-blockly
+          npm install
+          cd ..
+
+      - name: Link latest Blockly v12
+        run: |
+          cd core-blockly
+          npm run package
+          cd dist
+          npm link
+          cd ../../main
+          npm link blockly
+          cd ..
+
+      - name: Verify build
+        run: |
+          cd main
+          npm run build
+
   build:
+    name: Build test (against pinned v12)
+    # Don't run pinned version checks for PRs.
+    if: ${{ !github.base_ref }}
     runs-on: ubuntu-latest
     steps:
       - name: Checkout experimentation plugin
@@ -57,6 +105,7 @@ jobs:
           npm run build
 
   lint:
+    name: Eslint check
     timeout-minutes: 5
     runs-on: ubuntu-latest
     steps:
@@ -74,6 +123,7 @@ jobs:
         run: npm run lint
 
   format:
+    name: Prettier check
     timeout-minutes: 5
     runs-on: ubuntu-latest
     steps: