RFR: 7903915: JMH: Rebalance tests and test jobs parallelism

[Aleksey Shipilev]

The ongoing headache with some of the integration tests: some of them effectively test performance, so executing them in parallel introduces flaky failures. We can turn some of those tests serial, but then the testing time would explode on smaller machines, like we have in GHA. We can fix that by rebalancing our GHA test jobs.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jmh/pull/151/files
  Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=151&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903915
  Stats: 61 lines in 2 files changed: 42 ins; 8 del; 11 mod
  Patch: https://git.openjdk.org/jmh/pull/151.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/151/head:pull/151

PR: https://git.openjdk.org/jmh/pull/151