Bump Gradle plugin to 3.6.1 (#958)

Summary:
This is in line with the most recent stable Android Studio Release.
Pull Request resolved: https://github.com/facebook/flipper/pull/958

Test Plan:
Used it myself.

Open Source CI required a higher NDK, so let's first check what CI says to that internally now.

Reviewed By: jknoxville

Differential Revision: D20794634

Pulled By: passy

fbshipit-source-id: c32f934634b036ad3c1cad9fc49541e585d64329

.github/workflows/android-sample.yml

@@ -13,6 +13,8 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
+    - name: Install NDK 20
+      run: echo "y" | sudo /usr/local/lib/android/sdk/tools/bin/sdkmanager --install "ndk;20.0.5594570" --sdk_root=${ANDROID_SDK_ROOT}
     - name: Build with Gradle
       run: ./gradlew :sample:assembleDebug
     - name: upload artifact

.github/workflows/android.yml

@@ -15,6 +15,8 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
+    - name: Install NDK 20
+      run: echo "y" | sudo /usr/local/lib/android/sdk/tools/bin/sdkmanager --install "ndk;20.0.5594570" --sdk_root=${ANDROID_SDK_ROOT}
     - name: Build with Gradle
       run: ./gradlew :sample:assembleDebug :sample:assembleRelease
     - name: Rename apk