RFR: 8370667: TestPinnedGarbage.java intermittent trigger assert Region \d+ pinning status is inconsistent

[William Kemper]

This broke recently because we expanded the scope of the assertion to check all regions. However, there are times when the pin status for a region is only updated if the region belongs to the generation being collected. This change restores the previous behavior of the assertion.

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Commit messages:
 - Only verify region pins for collected generation

Changes: https://git.openjdk.org/jdk/pull/28027/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28027&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370667
  Stats: 13 lines in 4 files changed: 7 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/28027.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28027/head:pull/28027

PR: https://git.openjdk.org/jdk/pull/28027