pyproject(tool.mypy) Bump python_version 3.9 -> 3.10

See also:
- https://mypy.readthedocs.io/en/stable/config_file.html#confval-python_version
- Python 3.9 EOL:
  - https://devguide.python.org/versions/#:~:text=Release%20manager-,3.9,-PEP%20596
  - https://peps.python.org/pep-0596/

Author: tony

pyproject.toml

@@ -121,7 +121,7 @@ build-backend = "hatchling.build"
 
 [tool.mypy]
 strict = true
-python_version = "3.9"
+python_version = "3.10"
 files = [
   "src",
   "tests",