[SPARK-53630][PYTHON][DOCS][TESTS] Reenable doctest for Dataframe.freqItems

### What changes were proposed in this pull request?
Reenable doctest for `Dataframe.freqItems`, by make the example deterministic

### Why are the changes needed?
for test coverage and make sure the example is fine

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

### How was this patch tested?
ci

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

Closes #52380 from zhengruifeng/freq_item_sort.

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

Author: zhengruifeng

python/pyspark/sql/dataframe.py

@@ -5522,12 +5522,14 @@ def freqItems(
 
         Examples
         --------
+        >>> from pyspark.sql import functions as sf
         >>> df = spark.createDataFrame([(1, 11), (1, 11), (3, 10), (4, 8), (4, 8)], ["c1", "c2"])
-        >>> df.freqItems(["c1", "c2"]).show()  # doctest: +SKIP
+        >>> df = df.freqItems(["c1", "c2"])
+        >>> df.select([sf.sort_array(c).alias(c) for c in df.columns]).show()
         +------------+------------+
         |c1_freqItems|c2_freqItems|
         +------------+------------+
-        |   [4, 1, 3]| [8, 11, 10]|
+        |   [1, 3, 4]| [8, 10, 11]|
         +------------+------------+
         """
         ...