[jfx11u] RFR: 8274274: Update JUnit to version 5.8.1

[Kevin Rushforth]

Nearly clean backport to `jfx11u`. It isn't a clean backport since the mainline patch updated `gradle/verification-metadata.xml`, which doesn't exist in 11.

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Commit messages:
 - 8274274: Update JUnit to version 5.8.1

Changes: https://git.openjdk.java.net/jfx11u/pull/97/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=97&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274274
  Stats: 63 lines in 4 files changed: 58 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/97.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/97/head:pull/97

PR: https://git.openjdk.java.net/jfx11u/pull/97