RFR: 8334147: Shenandoah: Avoid taking lock for disabled free set logging

[William Kemper]

Not clean. Backport to only take lock for logging when log level is enabled.

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Commit messages:
 - Backport c47a0e005e54551e42ee1ae33d7169417a5f86d4

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/113/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=113&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334147
  Stats: 34 lines in 4 files changed: 13 ins; 11 del; 10 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/113.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/113/head:pull/113

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/113