[jdk21u-dev] RFR: 8316410: GC: Make TestCompressedClassFlags use createTestJvm

[Goetz Lindenmaier]

I backport this to keep the 21u test suite up-to-date. This will simplify future test backports.

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Commit messages:
 - Backport e649c563242a876a20007470c9412311ffa2a568

Changes: https://git.openjdk.org/jdk21u-dev/pull/43/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=43&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316410
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/43.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/43/head:pull/43

PR: https://git.openjdk.org/jdk21u-dev/pull/43