sdk: make test_batch_span_processor_scheduled_delay a bit more robust

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

Use assertAlmostEqual to accept a similar enough value (delta=1) and
avoid too big values.

Fix open-telemetry#3911

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

@@ -482,7 +482,7 @@ def test_batch_span_processor_scheduled_delay(self):
         self.assertTrue(export_event.wait(2))
         export_time = time.time()
         self.assertEqual(len(spans_names_list), 1)
-        self.assertGreaterEqual((export_time - start_time) * 1e3, 500)
+        self.assertAlmostEqual((export_time - start_time) * 1e3, 500, delta=1)
 
         span_processor.shutdown()