Add python 3.11 skimage's version matrix and remove warning for inputs data

[nzw0301]

Motivation

A part of https://github.com/optuna/optuna-examples/issues/164. Since scikit-image 0.2, local_binary_pattern shows a warning message if the images are float values because it internally converts images from int to float.

Description of the changes

• Add python 3.11 to skimage's version matrix
• Replace face dataset with digit dataset.