[doc] Fix sphinx build. (dmlc#8270)

Author: trivialfis

doc/requirements.txt

@@ -1,4 +1,4 @@
-sphinx>=4.4.0
+sphinx>=5.2.1
 mock
 sphinx_rtd_theme>=1.0.0
 breathe

doc/tutorials/spark_estimator.rst

@@ -61,6 +61,7 @@ SparkXGBClassifier
 pyspark classifier specific params, e.g. `raw_prediction_col` and `probability_col` parameters.
 Correspondingly, by default, `SparkXGBClassifierModel` transforming test dataset will
 generate result dataset with 3 new columns:
- - "prediction": represents the predicted label.
- - "raw_prediction": represents the output margin values.
- - "probability": represents the prediction probability on each label.
+
+- "prediction": represents the predicted label.
+- "raw_prediction": represents the output margin values.
+- "probability": represents the prediction probability on each label.