Integrated: 7904144: Update version to 8.3

[Christian Stein]

Please review this change to update jtreg's version to 8.3

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Commit messages:
 - 7904144: Update JTREG_VERSION to 8.3

Changes: https://git.openjdk.org/jtreg/pull/312/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=312&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904144
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/312.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/312/head:pull/312

PR: https://git.openjdk.org/jtreg/pull/312