graphics/jogamp-jogl: pin to java 8

After ignoring the faulty build.xml check which does not recognize that
JDK11 > JDK1.6, it gave an error for ${target.rt.jar} to set bootclasspath.

This port needs a maintainer or it might not survive a future prune of openjdk8.
But is has a port depending on this, so leave it for now.

PR: 272855
Approved-by: no maintainer