RFR: 7903721: Update version to 7.5

[Christian Stein]

The next promoted version of `jtreg` will be **7.5**.

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Commit messages:
 - 7903721: Update version to 7.5

Changes: https://git.openjdk.org/jtreg/pull/194/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=194&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903721
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/194.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/194/head:pull/194

PR: https://git.openjdk.org/jtreg/pull/194