[jdk21u-dev] RFR: 8317218: G1: Make TestG1HeapRegionSize 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 75b37e6d7ec285f1a954f9d5b16bf9e6b642f2fc

Changes: https://git.openjdk.org/jdk21u-dev/pull/48/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=48&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317218
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/48.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/48/head:pull/48

PR: https://git.openjdk.org/jdk21u-dev/pull/48