RFR: 8328269: NonFocusablePopupMenuTest.java should be marked as headful

[Jie Fu]

Please review this trivial change.
Thanks.

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Commit messages:
 - 8328269: NonFocusablePopupMenuTest.java should be marked as headful

Changes: https://git.openjdk.org/jdk/pull/18326/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18326&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328269
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18326.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18326/head:pull/18326

PR: https://git.openjdk.org/jdk/pull/18326