Install NDK 21.0.6113669

Author: AChep

.github/workflows/flutter.yml

@@ -23,8 +23,10 @@ jobs:
     - uses: actions/setup-java@v1
       with:
         java-version: '12.x'
-    - name: install NDK
+    - name: install NDK 20.0.5594570
       run: echo "y" | sudo ${ANDROID_HOME}/tools/bin/sdkmanager --install "ndk;20.0.5594570" --sdk_root=${ANDROID_SDK_ROOT}
+    - name: install NDK 21.0.6113669
+      run: echo "y" | sudo ${ANDROID_HOME}/tools/bin/sdkmanager --install "ndk;21.0.6113669" --sdk_root=${ANDROID_SDK_ROOT}
     - id: vars
       run: echo ::set-output name=tag::${GITHUB_REF:10}
     - uses: subosito/flutter-action@v1