[jdk17u-dev] RFR: 8271834: TestStringDeduplicationAgeThreshold intermittent failures on Shenandoah

[Aleksey Shipilev]

Clean backport to stabilize the tests and hopefully resolve some GHA 17u intermittent failures. I was not able to reproduce the failures locally, so I am backporting this blindly.

Additional testing:
 - [x] Linux x86_64 fastdebug, `gc/stringdedup` (20 repetitions)

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Commit messages:
 - Backport f9b2507f3e86bcb91e8ccfd0a84f31712fd535c2

Changes: https://git.openjdk.org/jdk17u-dev/pull/913/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=913&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8271834
  Stats: 49 lines in 1 file changed: 43 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/913.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/913/head:pull/913

PR: https://git.openjdk.org/jdk17u-dev/pull/913