xfail collision test on Windows (#542)

tiled/_tests/test_directory_walker.py

@@ -1,5 +1,4 @@
 import platform
-import time
 from pathlib import Path
 
 import pytest
@@ -24,6 +23,11 @@ def example_data_dir(tmpdir_factory):
     return tmpdir
 
 
+@pytest.mark.xfail(
+    platform.system() == "Windows",
+    reason="file cannot be removed while being used",
+    raises=PermissionError,
+)
 @pytest.mark.asyncio
 async def test_collision(example_data_dir, tmpdir):
     """Test that files which produce key collisions are ignored until the collision is resolved."""
@@ -40,12 +44,6 @@ async def test_collision(example_data_dir, tmpdir):
         # And omits the colliding entries.
         assert "a" not in client
 
-        # Windows will fail to unlink the file, below, if it is still being used:
-        # PermissionError: [WinError 32] The process cannot access the file because
-        # it is being used by another process: '...'
-        if platform.system() == "Windows":
-            time.sleep(5)
-
         # Resolve the collision.
         p.unlink()