Clarify the buildArg of GraalVM Native Image associated with `--initialize-at-build-time=org.junit.platform.engine.TestTag`

[linghengqian]

• In linghengqian-scratches/graalvm-trace-metadata-smoketest@ce78a1a , the --initialize-at-build-time=org.junit.platform.engine.TestTag parameter has been removed due to unit test refactoring.
• Whether the class related to the --initialize-at-build-time=org.junit.platform.engine.TestTag parameter has resolved the issue remains to be investigated.

graalvmNative {
    binaries {
        test {
            buildArgs.add('--initialize-at-build-time=org.junit.platform.engine.TestTag')
        }
    }
}

• Refer to Add support for org.apache.curator:curator-client:5.5.0 oracle/graalvm-reachability-metadata#381 .

[linghengqian]

• Check [GR-60258] Refactor JUnit feature graalvm/native-build-tools#693 .

[linghengqian]

Let me test this privately at some point.