RFR: 8352591: Missing UnlockDiagnosticVMOptions in VerifyGraphEdgesWithDeadCodeCheckFromSafepoints test

[Marc Chevalier]

Using `StressIGVN` in product requires `UnlockDiagnosticVMOptions`. My bad

Thanks,
Marc

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Commit messages:
 - Add UnlockDiagnosticVMOptions to VerifyGraphEdgesWithDeadCodeCheckFromSafepoints

Changes: https://git.openjdk.org/jdk/pull/24151/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24151&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352591
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24151.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24151/head:pull/24151

PR: https://git.openjdk.org/jdk/pull/24151