Added gradlew executable bit to default workflow

.github/workflows/main.yml

@@ -14,6 +14,9 @@ jobs:
       - uses: actions/setup-java@v1
         with: {java-version: 1.8}
 
+      - name: Make gradlew executable
+        run: chmod +x ./gradlew
+
       - name: Build release APK and AAB after tests
         id: unit_tests_and_build
         run: |