RFR: 8375367: vmTestbase tests reported variable ininitialized by clang23

[SendaoYan]

Hi all,

The local variable `dummy` is uninitialzed in function `static void JNICALL agentProc(jvmtiEnv* jvmti, JNIEnv* jni, void* arg)` at file test/hotspot/jtreg/vmTestbase/nsk/jvmti/scenarios/multienv/MA04/ma04t002/ma04t002[`].cpp. This PR initial the local variable `dummy` explicitly to avoid compiler warning by clang23.

Change has been verified locally by run the test entry test/hotspot/jtreg/vmTestbase/nsk/jvmti/scenarios/multienv/MA04/ma04t002/TestDescription.java. Test-fix only, no risk.

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Commit messages:
 - 8375367: vmTestbase tests reported variable ininitialized by clang23

Changes: https://git.openjdk.org/jdk/pull/29247/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29247&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375367
  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29247.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29247/head:pull/29247

PR: https://git.openjdk.org/jdk/pull/29247