GitHub Actions: Build Plugin zip, store as artifact on every PR (#26746)

.github/workflows/build-plugin-zip.yml

@@ -0,0 +1,47 @@
+name: Build Gutenberg Plugin Zip
+
+on:
+  pull_request:
+    paths-ignore:
+    - '**.md'
+  push:
+    branches: [master]
+    paths-ignore:
+    - '**.md'
+
+jobs:
+  build:
+    name: Build Release Artifact
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@master
+
+      - name: Cache node modules
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-node-modules
+        with:
+          # npm cache files are stored in `~/.npm` on Linux/macOS
+          path: ~/.npm
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+
+      - name: Use Node.js 12.x
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12.x
+
+      - name: Build Gutenberg plugin ZIP file
+        run: ./bin/build-plugin-zip.sh
+        env:
+          NO_CHECKS: 'true'
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: gutenberg-plugin
+          path: ./gutenberg.zip