fix test class split: move push exporter tests to separate class

The merge brought in push exporter plugin tests from #5128 which
ended up in TestCreatePullMetricReaders. Moved them to a new
TestCreateMetricReadersGeneral class with the _make_periodic_config
helper they need.

Assisted-by: Claude Opus 4.6

Author: MikeGoldsmith

opentelemetry-sdk/tests/_configuration/test_meter_provider.py

@@ -511,6 +511,20 @@ def test_pull_cardinality_limits_warns(self):
                 create_meter_provider(config)
         self.assertTrue(any("cardinality_limits" in msg for msg in cm.output))
 
+
+class TestCreateMetricReadersGeneral(unittest.TestCase):
+    @staticmethod
+    def _make_periodic_config(exporter_config):
+        return MeterProviderConfig(
+            readers=[
+                MetricReaderConfig(
+                    periodic=PeriodicMetricReaderConfig(
+                        exporter=exporter_config
+                    )
+                )
+            ]
+        )
+
     def test_no_reader_type_raises(self):
         config = MeterProviderConfig(readers=[MetricReaderConfig()])
         with self.assertRaises(ConfigurationError):