[SPARK-53632][PYTHON][DOCS][TESTS] Reenable doctest for DataFrame.pandas_api

### What changes were proposed in this pull request?
Reenable doctest for `DataFrame.pandas_api`

### Why are the changes needed?
for test coverage, the doctest will be ran when pandas and pyarrow are installed

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ci

### Was this patch authored or co-authored using generative AI tooling?
no

Closes #52383 from zhengruifeng/doc_test_pandas_api.

Authored-by: Ruifeng Zheng <[email protected]>
Signed-off-by: Ruifeng Zheng <[email protected]>

Author: zhengruifeng

python/pyspark/sql/classic/dataframe.py

@@ -1949,6 +1949,7 @@ def _test() -> None:
         del pyspark.sql.dataframe.DataFrame.toPandas.__doc__
         del pyspark.sql.dataframe.DataFrame.mapInArrow.__doc__
         del pyspark.sql.dataframe.DataFrame.mapInPandas.__doc__
+        del pyspark.sql.dataframe.DataFrame.pandas_api.__doc__
 
     spark = (
         SparkSession.builder.master("local[4]").appName("sql.classic.dataframe tests").getOrCreate()

python/pyspark/sql/connect/dataframe.py

@@ -2321,6 +2321,7 @@ def _test() -> None:
         del pyspark.sql.dataframe.DataFrame.toPandas.__doc__
         del pyspark.sql.dataframe.DataFrame.mapInArrow.__doc__
         del pyspark.sql.dataframe.DataFrame.mapInPandas.__doc__
+        del pyspark.sql.dataframe.DataFrame.pandas_api.__doc__
 
     globs["spark"] = (
         PySparkSession.builder.appName("sql.connect.dataframe tests")

python/pyspark/sql/dataframe.py

@@ -6295,15 +6295,15 @@ def pandas_api(
         >>> df = spark.createDataFrame(
         ...     [(14, "Tom"), (23, "Alice"), (16, "Bob")], ["age", "name"])
 
-        >>> df.pandas_api()  # doctest: +SKIP
+        >>> df.pandas_api()
            age   name
         0   14    Tom
         1   23  Alice
         2   16    Bob
 
         We can specify the index columns.
 
-        >>> df.pandas_api(index_col="age")  # doctest: +SKIP
+        >>> df.pandas_api(index_col="age")
               name
         age
         14     Tom