RFR: 8346688: GenShen: Missing metadata trigger log message

[William Kemper]

Clean backport. Logging changes only. Fixes tests.

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Commit messages:
 - Backport b8e40b9c2dfecdad9096015c1aa208ea077db7f5

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/149/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346688
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/149.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/149/head:pull/149

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/149