Update Javadoc deeps link to Java 11

[TimvdLippe]

We currently use Java 6 to deeplink to the JDK and the URL no longer shows the necessary element-list, which is why it currently fails the build: https://github.com/mockito/mockito/actions/runs/3100073977/jobs/5019939573#step:7:229

[marcphilipp]

Why not deep link against JDK 8 since that's the baseline?

[TimvdLippe]

@marcphilipp The problem is not the Oracle version of the JDK, but the JDK version that we use for the javadoc tool. https://docs.oracle.com/javase/8/docs/api/element-list is missing as well, but https://docs.oracle.com/javase/8/docs/api/package-list does exist. Therefore, we have to use JDK 11+ for the generation of our Javadoc if we want to fix this issue, as that one is aware of package-list and understands how to use it.

[marcphilipp]

FWIW we have this workaround in the JUnit build:
https://github.com/junit-team/junit5/blob/517bfd56ad8ba8d22609b5055f4bb46a3d38c953/documentation/documentation.gradle.kts#L307-L320

[TimvdLippe]

Superseded by #2766