RFR: 8330071: GenShen: Allow old to expand again at end of each GC

[Kelvin Nilsen]

This pull request contains a backport of commit 0578af80 from the openjdk/shenandoah repository.

The commit being backported was authored by Kelvin Nilsen on 15 Apr 2024 and was reviewed by William Kemper and Y. Srinivas Ramakrishna.

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Commit messages:
 - Backport 0578af8015bc0dfcd4a2b726b1a8b52f68712cf2

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/35/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=35&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330071
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/35.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/35/head:pull/35

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/35