TST: xfail the windows font test

1. we are moving to registry only for finding fonts on windows
2. our test just drops the font in the correct directory
3. this is not enough to get the registry to agree it is there

We will xfail this test for now.

Author: tacaswell

lib/matplotlib/tests/test_font_manager.py

@@ -200,7 +200,7 @@ def test_user_fonts_win32():
         pytest.xfail("This test should only run on CI (appveyor or azure) "
                      "as the developer's font directory should remain "
                      "unchanged.")
-
+    pytest.xfail("We need to update the registry for this test to work")
     font_test_file = 'mpltest.ttf'
 
     # Precondition: the test font should not be available