Github Actions: Build with Gradle 6.9
Github Actions: Build with Gradle 6.9

Use the `gradle/gradle-build-action` to build with a specified
version of Gradle. In our case, let’s use Gradle 6.9.


bitcoinj/bitcoinj,yenliangl/bitcoinj,natzei/bitcoinj,bitcoinj/bitcoinj,natzei/bitcoinj,yenliangl/bitcoinj