RFR: 8361529: GenShen: Fix bad assert in swap card tables [v2]

[William Kemper]

> Clean backport. Fixes assertion logic.

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'shenandoah-jdk21u/master' into fix-card-table-assert-21
 - Backport 1de2acea77da57fd44b214332a73cc6621806e4d

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Changes:
  - all: https://git.openjdk.org/shenandoah-jdk21u/pull/203/files
  - new: https://git.openjdk.org/shenandoah-jdk21u/pull/203/files/865c27e5..52814297

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=203&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=203&range=00-01

  Stats: 194 lines in 19 files changed: 88 ins; 36 del; 70 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/203.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/203/head:pull/203

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/203