Use tomllib from the standard library on Python 3.11+

Fallback to tomli, which has the same API.

Fixes tox-dev#2462

Author: hroncok

setup.cfg

@@ -39,7 +39,7 @@ install_requires =
     pluggy>=0.12.0
     py>=1.4.17
     six>=1.14.0 # required when virtualenv>=20
-    toml>=0.9.4
+    tomli;python_version<"3.11"
     virtualenv!=20.0.0,!=20.0.1,!=20.0.2,!=20.0.3,!=20.0.4,!=20.0.5,!=20.0.6,!=20.0.7,>=16.0.0
     colorama>=0.4.1 ;platform_system=="Windows"
     importlib-metadata>=0.12;python_version<"3.8"

src/tox/config/__init__.py

@@ -20,7 +20,12 @@
 import pluggy
 import py
 import six
-import toml
+
+if sys.version_info >= (3, 11):
+    import tomllib
+else:
+    import tomli as tomllib
+
 from packaging import requirements
 from packaging.utils import canonicalize_name
 from packaging.version import Version
@@ -304,8 +309,8 @@ def parseconfig(args, plugins=()):
 
 
 def get_py_project_toml(path):
-    with io.open(str(path), encoding="UTF-8") as file_handler:
-        config_data = toml.load(file_handler)
+    with io.open(str(path), mode="rb") as file_handler:
+        config_data = tomllib.load(file_handler)
         return config_data