Make test_multi_polygon_column work independently of which factory the store uses

Author: keithdoggett

test/cases/adapters/postgresql/postgis_test.rb

@@ -169,7 +169,7 @@ def test_multi_polygon_column
     rec.m_poly = wkt
     assert rec.save
     rec = klass.find(rec.id) # force reload
-    assert rec.m_poly.is_a?(RGeo::Geos::CAPIMultiPolygonImpl)
+    assert RGeo::Feature::MultiPolygon.check_type(rec.m_poly)
     assert_equal wkt, rec.m_poly.to_s
   end