[jdk21u-dev] RFR: 8317188: G1: Make TestG1ConcRefinementThreads use createTestJvm

[Goetz Lindenmaier]

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

-------------

Commit messages:
 - Backport a949824e98a8872645f292c9cc9ed2fe1cccadce

Changes: https://git.openjdk.org/jdk21u-dev/pull/47/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=47&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317188
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/47.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/47/head:pull/47

PR: https://git.openjdk.org/jdk21u-dev/pull/47