Skip test_double_start_finished on Windows.

It seems the process sometimes crashes...

tests/misc/test_guiprocess.py

@@ -21,6 +21,7 @@
 
 """Tests for qutebrowser.misc.guiprocess."""
 
+import os
 import sys
 import textwrap
 import logging
@@ -98,6 +99,7 @@ def test_double_start(qtbot, proc):
 
 
 @pytest.mark.not_frozen
+@pytest.mark.skipif(os.name == 'nt', reason="Test is flaky on Windows...")
 def test_double_start_finished(qtbot, proc):
     """Test starting a GUIProcess twice (with the first call finished)."""
     with qtbot.waitSignals([proc.started, proc.finished], raising=True,