Increase available memory for nightly builds and use G1GC

Copy settings from EXA.
They are failing with OutOfMemoryError.

Author: bmarty

.github/workflows/nightly.yml

@@ -7,7 +7,7 @@ on:
     - cron: "0 4 * * *"
 
 env:
-  GRADLE_OPTS: -Dorg.gradle.jvmargs="-Xmx3072m -Dfile.encoding=UTF-8 -XX:+HeapDumpOnOutOfMemoryError -XX:MaxMetaspaceSize=1g" -Dkotlin.daemon.jvm.options="-Xmx2560m" -Dkotlin.incremental=false
+  GRADLE_OPTS: -Dorg.gradle.jvmargs="-Xmx6g -Dfile.encoding=UTF-8 -XX:+HeapDumpOnOutOfMemoryError -XX:MaxMetaspaceSize=1g" -Dkotlin.incremental=false -XX:+UseG1GC
   CI_GRADLE_ARG_PROPERTIES: --stacktrace -PpreDexEnable=false --max-workers 2 --no-daemon
 
 jobs: