RFR: 8310024: Skip failing scene change tests on macOS

[Kevin Rushforth]

Simple fix to skip two failing tests on macOS until the underlying bugs are fixed:

SceneChangeEventsTest::testSceneChange -- [JDK-8300094](https://bugs.openjdk.org/browse/JDK-8300094)
SceneChangeShouldNotFocusStageTest::windowShouldRemainIconified -- [JDK-8305675](https://bugs.openjdk.org/browse/JDK-8305675)

With this patch, we now get a clean test run on macOS 12 and 13.

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Commit messages:
 - 8310024: Skip failing scene change tests on macOS

Changes: https://git.openjdk.org/jfx/pull/1153/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1153&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310024
  Stats: 13 lines in 2 files changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1153.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1153/head:pull/1153

PR: https://git.openjdk.org/jfx/pull/1153