sdk: skip test_batch_span_processor_scheduled_delay on pypy / windows

It happened that tests failed because the delay was fired some
microseconds earlier:

>       self.assertGreaterEqual((export_time - start_time) * 1e3, 500)
E       AssertionError: 499.9737739562988 not greater than or equal to 500

We should probably revise all these skip on Windows Pypy once we have a
Python 3.9 baseline and Pypy >= 7.3.12.

Fix #3911

opentelemetry-sdk/tests/trace/export/test_export.py

@@ -461,6 +461,10 @@ def _target():
 
         span_processor.shutdown()
 
+    @mark.skipif(
+        python_implementation() == "PyPy" and system() == "Windows",
+        reason="This test randomly fails in Windows with PyPy",
+    )
     def test_batch_span_processor_scheduled_delay(self):
         """Test that spans are exported each schedule_delay_millis"""
         spans_names_list = []