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

[Albert Mingkun Yang]

On Thu, 4 Apr 2024 11:55:00 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Add colon and Time Format details expected in log messages to the test. Some tools require that these details are maintained.
> 
> Testing: tier1

Marked as reviewed by ayang (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/18623#pullrequestreview-1994265104