RFR: 7904004: Run jtreg GHA workflows for FreeBSD

[snake66]

GitHub Actions does not natively support FreeBSD, so we use the vmactions/freebsd-vm action as a base to run the tests in a VM under an Ubuntu runner.

This work is sponsored by The FreeBSD Foundation.

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Commit messages:
 - 7904004: Run jtreg GHA workflows for FreeBSD

Changes: https://git.openjdk.org/jtreg/pull/262/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=262&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904004
  Stats: 27 lines in 1 file changed: 27 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/262.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/262/head:pull/262

PR: https://git.openjdk.org/jtreg/pull/262