RFR: 7904070: Update to use JUnit 5.13.4

[Christian Stein]

On Mon, 1 Sep 2025 08:35:56 GMT, Christian Stein <cstein at openjdk.org> wrote:

> Please review this change updating the JUnit version to [5.13.4](https://docs.junit.org/current/release-notes/index.html#release-notes-5.13.4).

> `JUnit 5 = JUnit Platform 1.y.z + JUnit Jupiter 5.y.z + JUnit Vintage 5.y.z`

Yes, it's a source of confusion that won't be missed with the upcoming JUnit 6 releases: there, all artifacts will have the same major version number.

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PR Comment: https://git.openjdk.org/jtreg/pull/282#issuecomment-3241703147