update test expectations (don't convert to float64 when Int64 or UInt64 does the trick)

Author: angela-tarantula

pandas/tests/frame/methods/test_combine_first.py

@@ -475,6 +475,7 @@ def test_combine_first_with_nan_multiindex():
             "d": [1.0, 4.0, np.nan, 2.0, 5.0, np.nan, np.nan, 3.0, np.nan, 6.0, np.nan],
         },
         index=mi_expected,
+        dtype="Int64",
     )
     tm.assert_frame_equal(res, expected)
 
@@ -521,6 +522,7 @@ def test_combine_first_duplicates_rows_for_nan_index_values():
         index=MultiIndex.from_arrays(
             [[1, 2, 3, 4], [np.nan, 5, 6, 7]], names=["a", "b"]
         ),
+        dtype="Int64",
     )
     combined = df1.combine_first(df2)
     tm.assert_frame_equal(combined, expected)