### What changes were proposed in this pull request?
This PR is a small followup of https://github.com/apache/spark/pull/28793 and proposes to use `is_categorical_dtype` instead of deprecated `is_categorical`.
`is_categorical_dtype` exists from minimum pandas version we support (https://github.com/pandas-dev/pandas/blob/v0.23.2/pandas/core/dtypes/api.py), and `is_categorical` was deprecated from pandas 1.1.0 (87a1cc21ca).
### Why are the changes needed?
To avoid using deprecated APIs, and remove warnings.
### Does this PR introduce _any_ user-facing change?
Yes, it will remove warnings that says `is_categorical` is deprecated.
### How was this patch tested?
By running any pandas UDF with pandas 1.1.0+:
```python
import pandas as pd
from pyspark.sql.functions import pandas_udf
def func(x: pd.Series) -> pd.Series:
return x
spark.range(10).select(pandas_udf(func, "long")("id")).show()
```
Before:
```
/.../python/lib/pyspark.zip/pyspark/sql/pandas/serializers.py:151: FutureWarning: is_categorical is deprecated and will be removed in a future version. Use is_categorical_dtype instead
...
```
After:
```
...
```
Closes#30114 from HyukjinKwon/replace-deprecated-is_categorical.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Bryan Cutler <cutlerb@gmail.com>
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