GitHub Actions: add special case for Gradle 4.10/JDK11/Ubuntu
GitHub Actions: add special case for Gradle 4.10/JDK11/Ubuntu

This is the “closest” Github Actions config we can get to our
target Debian build (Debian Bullseye/JDK11/Debian Gradle 4.4).

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