RFR: 8310846: Skip failing test InitialWindowSizeTest on Linux

[Michael Strauß]

Skips `InitialWindowSizeTest` on Linux until [JDK-8310845](https://bugs.openjdk.org/browse/JDK-8310845) is fixed.

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Commit messages:
 - Skip test on Linux

Changes: https://git.openjdk.org/jfx/pull/1162/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1162&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310846
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1162.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1162/head:pull/1162

PR: https://git.openjdk.org/jfx/pull/1162