RFR: 8352641: [TESTBUG] VerifyGraphEdgesWithDeadCodeCheckFromSafepoints.java fails due to missing UnlockDiagnosticVMOptions

[Fei Yang]

Hi, please review this trivial change fixing a test bug.

The test reports following error message when running with release build.
`Error: VM option 'StressIGVN' is diagnostic and must be enabled via -XX:+UnlockDiagnosticVMOptions.`
This adds the needed UnlockDiagnosticVMOptions option for this test. Same test passes with this extra option.

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Commit messages:
 - 8352641: [TESTBUG] VerifyGraphEdgesWithDeadCodeCheckFromSafepoints.java fails due to missing UnlockDiagnosticVMOptions

Changes: https://git.openjdk.org/jdk/pull/24173/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24173&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352641
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24173.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24173/head:pull/24173

PR: https://git.openjdk.org/jdk/pull/24173