RFR: 8346690: Shenandoah: Fix log message for end of GC usage report

[William Kemper]

Clean backport. Logging changes only.

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Commit messages:
 - Backport d2a48634b872b65668b57d3975f805277ae96f83

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/148/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=148&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346690
  Stats: 18 lines in 1 file changed: 3 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/148.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/148/head:pull/148

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/148