RFR: 7904024: jcstress: Update concurrency mailing list in README.md

[Pavel Rappo]

In addition to updating the concurrency mailing list [^1], I also updated the address for this project's list [^2] [^3].

[^1]: https://mail.openjdk.org/pipermail/jcstress-dev/2025-June/001294.html
[^2]: https://mail.openjdk.org/pipermail/announce/2022-May/000318.html
[^3]: https://mail.openjdk.org/pipermail/announce/2022-June/000321.html

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Commit messages:
 - Update mailing lists

Changes: https://git.openjdk.org/jcstress/pull/163/files
  Webrev: https://webrevs.openjdk.org/?repo=jcstress&pr=163&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904024
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jcstress/pull/163.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/163/head:pull/163

PR: https://git.openjdk.org/jcstress/pull/163