RFR: 8378164: test/jdk/java/net/httpclient/http3/*.java: convert tests that use ITestContext to JUnit [v3]

[Daniel Fuchs]

> Similar to https://github.com/openjdk/jdk/pull/29786 - this time with HTTP/3 tests.

Daniel Fuchs has updated the pull request incrementally with two additional commits since the last revision:

 - Update test/jdk/java/net/httpclient/http3/PostHTTP3Test.java
   
   Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>
 - Update test/jdk/java/net/httpclient/http3/GetHTTP3Test.java
   
   Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29824/files
  - new: https://git.openjdk.org/jdk/pull/29824/files/31ad86bf..197f8730

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29824&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29824&range=01-02

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29824.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29824/head:pull/29824

PR: https://git.openjdk.org/jdk/pull/29824