Disable Gradle daemon in CI

[reline]

Appending --no-daemon to each gradle build in the CI config is tedious, set it globally in the environment.

Via environment variables: add the flag -Dorg.gradle.daemon=false to the GRADLE_OPTS environment variable

https://docs.gradle.org/6.8-rc-1/userguide/gradle_daemon.html#sec:ways_to_disable_gradle_daemon

[reline]

Set the max workers to 4 globally as well while we're at it.