Make sure that we always publish binaries using Java 8

[hamzaremmal]

For now, we hardcode the Java version to use when publishing the binaries to Maven in the CI configuration.
#20018 added a warning in this file to prevent accidental modification of the Java version. Nevertheless, we should consider even stronger mecanism to protect against accidental modifications. @WojciechMazur in #19750 proposed to change he configuration in sbt to make sure that we also release java-8 binaries, no matter what java version we are use in the CI.

This issue is a follow up of #19750 (since the other will be closed by #20018)