[skip ci] Split push and PR build workflows so they don't cancel each other

.github/workflows/build_pull_request.yml

@@ -0,0 +1,33 @@
+name: PR build check
+on:
+  pull_request:
+
+jobs:
+  build:
+    name: Build app
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Clone repo
+        uses: actions/checkout@v2
+
+      - name: Validate Gradle Wrapper
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Set up JDK 11
+        uses: actions/setup-java@v1
+        with:
+          java-version: 11
+
+      - name: Copy CI gradle.properties
+        run: |
+          mkdir -p ~/.gradle
+          cp .github/runner-files/ci-gradle.properties ~/.gradle/gradle.properties
+
+      - name: Build app
+        uses: eskatos/gradle-command-action@v1
+        with:
+          arguments: assembleStandardRelease
+          wrapper-cache-enabled: true
+          dependencies-cache-enabled: true
+          configuration-cache-enabled: true