Create Android workflow

.github/workflows/android.yml

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+name: Android CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Fix gradlew permission
+      run: chmod +x gradlew
+    - name: Check
+      run: ./gradlew check --stacktrace
+    - name: Assemble
+      run: ./gradlew assembleDebug bundleDebug --stacktrace
+    - name: Upload APK
+      uses: actions/upload-artifact@v2
+      with:
+        name: app-debug.apk
+        path: app/build/outputs/apk/debug/app-debug.apk
+    - name: Upload AAB
+      uses: actions/upload-artifact@v2
+      with:
+        name: app-debug.aab
+        path: app/build/outputs/bundle/debug/app-debug.aab