RFR: 8296928: Fix failing string table test after log changes

[Stefan Johansson]

Please review this fix for a failing test that expects ZGC logging to look a certain way. 

Updated the log-messages to match the current state of things.

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Commit messages:
 - Fix for failing string-table test

Changes: https://git.openjdk.org/zgc/pull/9/files
 Webrev: https://webrevs.openjdk.org/?repo=zgc&pr=9&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296928
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/zgc/pull/9.diff
  Fetch: git fetch https://git.openjdk.org/zgc pull/9/head:pull/9

PR: https://git.openjdk.org/zgc/pull/9