[jdk26u] RFR: 8373869: Refactor java/net/httpclient/ThrowingPushPromises*.java tests to use JUnit5

[Hari Prasad Kummari]

Tested local changes and no failure is observed.

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Commit messages:
 - backport e5ca77838b9243321ed66afc2f460378d25add63

Changes: https://git.openjdk.org/jdk26u/pull/65/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk26u&pr=65&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373869
  Stats: 158 lines in 8 files changed: 51 ins; 39 del; 68 mod
  Patch: https://git.openjdk.org/jdk26u/pull/65.diff
  Fetch: git fetch https://git.openjdk.org/jdk26u.git pull/65/head:pull/65

PR: https://git.openjdk.org/jdk26u/pull/65