DOC: suppress warnings from CategoricalBlock deprecation (pandas-dev#40542)

Author: jbrockmendel

doc/source/user_guide/io.rst

@@ -5240,6 +5240,7 @@ Write to a feather file.
 Read from a feather file.
 
 .. ipython:: python
+   :okwarning:
 
    result = pd.read_feather("example.feather")
    result
@@ -5323,6 +5324,7 @@ Write to a parquet file.
 Read from a parquet file.
 
 .. ipython:: python
+   :okwarning:
 
    result = pd.read_parquet("example_fp.parquet", engine="fastparquet")
    result = pd.read_parquet("example_pa.parquet", engine="pyarrow")