RFR: 8362379: Test serviceability/HeapDump/UnmountedVThreadNativeMethodAtTop.java should mark as /native

[SendaoYan]

Hi all,

  Test serviceability/HeapDump/UnmountedVThreadNativeMethodAtTop.java call native libary 'UnmountedVThreadNativeMethodAtTop' with System.loadLibrary. If run this test without jtreg option '-nativepath', jtreg will report 'JUnit test failure'. After this PR, we add jtreg directive `/native` to test header, run this test without jtreg option '-nativepath', jtreg will report 'Error. Use -nativepath to specify the location of native code'. So add `/native` directive will make this test more friendly.

Change has been verified locally, test-fix only, no risk.

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Commit messages:
 - 8362379: Test serviceability/HeapDump/UnmountedVThreadNativeMethodAtTop.java should mark as /native

Changes: https://git.openjdk.org/jdk/pull/26384/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26384&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8362379
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26384.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26384/head:pull/26384

PR: https://git.openjdk.org/jdk/pull/26384