[SPARK-43960][PS][TESTS] DataFrameConversionTestsMixin is not tested properly

### What changes were proposed in this pull request?

This PR proposes to fix test which is not tested properly.

### Why are the changes needed?

To test properly.

### Does this PR introduce _any_ user-facing change?

No, it's test only

### How was this patch tested?

The existing CI should pass

Closes #41450 from itholic/SPARK-43960.

Authored-by: itholic <haejoon.lee@databricks.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>
diff --git a/python/pyspark/pandas/tests/test_dataframe_conversion.py b/python/pyspark/pandas/tests/test_dataframe_conversion.py
index 5b57b19..d245b44 100644
--- a/python/pyspark/pandas/tests/test_dataframe_conversion.py
+++ b/python/pyspark/pandas/tests/test_dataframe_conversion.py
@@ -263,7 +263,9 @@
         )
 
 
-class DataFrameConversionTests(ComparisonTestBase, SQLTestUtils, TestUtils):
+class DataFrameConversionTests(
+    DataFrameConversionTestsMixin, ComparisonTestBase, SQLTestUtils, TestUtils
+):
     pass