[jdk17u-dev] RFR: 8301704: Shorten the number of GCs in UnloadingTest.java to verify a class loader not being unloaded

[Amos Shi]

Backport of [JDK-8301704](https://bugs.openjdk.org/browse/JDK-8301704)

Testing
- Local: Test passed on MacOS 14.5
  - `UnloadingTest.java`: Test results: passed: 1
- Pipeline: 
- Testing Machine:

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Commit messages:
 - Backport c8cc7b67dbb4633e365a5d6e44419775ebce9d4a

Changes: https://git.openjdk.org/jdk17u-dev/pull/2583/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2583&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301704
  Stats: 36 lines in 2 files changed: 29 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2583.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2583/head:pull/2583

PR: https://git.openjdk.org/jdk17u-dev/pull/2583