Tests in gradle do not run with "--illegal-access=deny" like in 8.x

In LUCENE-8035 we added --illegal-access=deny to the JVM options to enfoce that no code is using any internal JDK APIs.

https://github.com/apache/lucene-solr/blob/branch_8x/lucene/common-build.xml#L1053-L1055

While changing to Gradle we lost this option somehow. We need to add it back, as JDK 16 or latest JDK 17 will default to this setting anyways, so we should again make sure that testing works under restricted conditions! Here is the JEP: https://openjdk.java.net/jeps/396