[jdk11u] RFR: 8315529: [11u] Exclude some failing Z-GC tests

[Christoph Langer]

There are two constantly failing Z-GC tests (in one of our/SAP's Linux x64 CI configurations).

Since Z-GC is experimental in 11 and thus probably not highly utilized, we should exclude the tests for now.

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Commit messages:
 - JDK-8315529

Changes: https://git.openjdk.org/jdk11u/pull/80/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u&pr=80&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315529
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u/pull/80.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u.git pull/80/head:pull/80

PR: https://git.openjdk.org/jdk11u/pull/80