RFR: 8378565: Refactor test/jdk/java/net/httpclient/http3/*.java TestNG tests to JUnit

[Daniel Fuchs]

This is a followup from https://github.com/openjdk/jdk/pull/29850, this time converting all (but one) TestNG tests under `test/jdk/java/net/httpclient/http3/` to use JUnit

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Commit messages:
 - 8378565: Refactor test/jdk/java/net/httpclient/http3/*.java TestNG tests to JUnit

Changes: https://git.openjdk.org/jdk/pull/29893/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29893&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378565
  Stats: 589 lines in 28 files changed: 99 ins; 84 del; 406 mod
  Patch: https://git.openjdk.org/jdk/pull/29893.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29893/head:pull/29893

PR: https://git.openjdk.org/jdk/pull/29893