chore: use if TYPE_CHECKING: blocks (#2866)

unit_test/main_tests/main_platform_test.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import sys
 
 import pytest
@@ -5,10 +7,14 @@ import pytest
 from cibuildwheel.__main__ import main
 from cibuildwheel.architecture import Architecture
 from cibuildwheel.selector import EnableGroup
-from cibuildwheel.typing import PlatformName
 
 from ..conftest import MOCK_PACKAGE_DIR
-from .conftest import ArgsInterceptor
+
+TYPE_CHECKING = False
+if TYPE_CHECKING:
+    from cibuildwheel.typing import PlatformName
+
+    from .conftest import ArgsInterceptor
 
 
 @pytest.mark.parametrize("option_value", [None, "auto", ""])