Tweaks to support building with OpenJDK 21.0.2; no functional changes

[bluedenim]

Some uses of Powermock in the unit tests are running into errors like:

java.lang.reflect.InaccessibleObjectException: Unable to make private final native void java.lang.Object.wait0(long) 
throws java.lang.InterruptedException accessible: module java.base does not "opens java.lang"
to unnamed module @6debcae2

Adding a plug-in entry for maven-surefire-plugin with --add-opens java.base/java.lang=ALL-UNNAMED (among others) seems to do the trick.