science/opensim-core: pin to openjdk8

Does not build with jdk11+:
[00:00:23] CMake Error at /usr/local/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:233 (message):
[00:00:23] Could NOT find JNI (missing: JAVA_INCLUDE_PATH2 AWT) (Required is at least
[00:00:23] version "1.7")

PR: 291719
Approved-By: maintainer timeout