fix review

Signed-off-by: yaommen <myanstu@163.com>

Author: myandpr

doc/source/data/loading-data.rst

@@ -478,6 +478,7 @@ Ray Data interoperates with libraries like pandas, NumPy, and Arrow.
                 "food": ["spam", "ham", "eggs"],
                 "price": [9.34, 5.37, 0.94]
             })
+            df["food"] = df["food"].astype("string")
             ds = ray.data.from_pandas(df)
 
             print(ds)