RFR: 8339703: Problem list serviceability/sa/TestJhsdbJstackUpcall.java for generational ZGC

[Chris Plummer]

This is a new SA test. We don't support SA with generational ZGC, so the test needs to be problem listed. 

Note there is also a failure with regular ZGC, but I think that can be addressed in the test (it's looking for the thread name, which can't be found with ZGC). For regular ZGC I'm either going to fix the test or problem list it under a different CR depending on how testing of my simple fix turns out.

I'd like to push this as a trivial change.

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Commit messages:
 - Problemlist TestJhsdbJstackUpcall.java for gen ZGC

Changes: https://git.openjdk.org/jdk/pull/20902/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20902&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339703
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20902.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20902/head:pull/20902

PR: https://git.openjdk.org/jdk/pull/20902