RFR: 8329660: G1: Improve TestGCLogMessages to be more precise

[Ivan Walulya]

Add colon and Time Format details expected in log messages to the test. Some tools require that these details are maintained.

Testing: tier1

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/18623/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18623&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329660
  Stats: 72 lines in 2 files changed: 0 ins; 0 del; 72 mod
  Patch: https://git.openjdk.org/jdk/pull/18623.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18623/head:pull/18623

PR: https://git.openjdk.org/jdk/pull/18623