refactor: tomllib in _compat

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

unit_test/main_tests/main_options_test.py

@@ -6,12 +6,8 @@ from pathlib import Path
 
 import pytest
 
-if sys.version_info >= (3, 11):
-    import tomllib
-else:
-    import tomli as tomllib
-
 from cibuildwheel.__main__ import main
+from cibuildwheel._compat import tomllib
 from cibuildwheel.environment import ParsedEnvironment
 from cibuildwheel.options import BuildOptions, _get_pinned_container_images
 from cibuildwheel.util import BuildSelector, resources_dir, split_config_settings