CI: add/update PR build action

Author: hinerm

.github/workflows/build-pr.yml

@@ -0,0 +1,35 @@
+name: build PR
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Cache m2 folder
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-m2
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-build-${{ env.cache-name }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          java-version: '8'
+          distribution: 'zulu'
+      - name: Set up CI environment
+        run: .github/setup.sh
+      - name: Execute the build
+        run: .github/build.sh