RFR: 8369488: Update to use jtreg 8.1

[Christian Stein]

On Thu, 9 Oct 2025 09:34:11 GMT, Christian Stein <cstein at openjdk.org> wrote:

> Please review the change to update to using jtreg `8.1`.
> 
> The primary change is to the `jib-profiles.js` file, which specifies the version of jtreg to use, for those systems that rely on this file. In addition, the `requiredVersion` has been updated in the various `TEST.ROOT` files.

Usually @shipilev is kind and quick to provide them here: https://builds.shipilev.net/jtreg/

Mind his warning and motto, though:
> WARNING: These artifacts are not well-tested, not virus-checked, may contain horrible bugs that could lead to data corruption, engulfing machines in flames, sharing your financial data, selling your pets on eBay, etc. etc. etc. everything that applies for binaries^W code^W anything downloaded from the Internet. Be cautious. If in doubt, build from the source yourself, and/or run on staging environment that is not painful to restore.
>

> Our motto: "[builds.shipilev.net](https://builds.shipilev.net/) — still more secure than npm install"

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PR Comment: https://git.openjdk.org/jdk/pull/27719#issuecomment-3390690779