[jdk25u] RFR: 8361950: Update to use jtreg 8

[Aleksey Shipilev]

On Mon, 6 Oct 2025 15:29:15 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Upgrading jtreg to 8 to match mainline. It is a separate commit, so that we can backout jtreg 8 upgrade separately, if we need.
> 
> Additional testing:
>  - [x] GHA
>  - [x] Linux AArch64 server fastdebug, `all` with jtreg-8+2

Push approval granted.

-------------

PR Comment: https://git.openjdk.org/jdk25u/pull/269#issuecomment-3382146335