RFR: 7903891: jcstress: Switch to latest runner versions

[Aleksey Shipilev]

We always playing the catchup game with runners. Let's just default to latest runners for every OS flavor.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jcstress/pull/154/files
  Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=154&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903891
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jcstress/pull/154.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/154/head:pull/154

PR: https://git.openjdk.org/jcstress/pull/154