Mark known failure test on Windows.

Closes gh-4907

IPython/core/tests/test_run.py

@@ -495,6 +495,7 b' def test_run_tb():'
         nt.assert_in("RuntimeError", out)
         nt.assert_equal(out.count("---->"), 3)
 
[e-mail](sys.platform == 'win32', "writes to io.stdout aren't captured on Windows")
 def test_script_tb():
     """Test traceback offset in `ipython script.py`"""
     with TemporaryDirectory() as td: