RFR: 8299044 : test/jdk/javax/swing/JComboBox/JComboBoxBorderTest.java fails on non mac

[lawrence.andrews]

This test needs to be executed on mac os only

@shurymury 
@honkar-jdk

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Commit messages:
 - 8299044 : test/jdk/javax/swing/JComboBox/JComboBoxBorderTest.java fails on non mac

Changes: https://git.openjdk.org/jdk/pull/11730/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11730&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299044
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11730.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11730/head:pull/11730

PR: https://git.openjdk.org/jdk/pull/11730