RFR: 8329789: GenShen: Over assertive assert when scanning remembered set [v2]

[William Kemper]

> When scanning the remembered set for update-refs, it is possible for the scanner to encounter a card that was dirtied by a mutator during the scan. This is by design.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Finish comment

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/418/files
  - new: https://git.openjdk.org/shenandoah/pull/418/files/7bd0251e..c4e0be2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=418&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=418&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/shenandoah/pull/418.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/418/head:pull/418

PR: https://git.openjdk.org/shenandoah/pull/418