Monkeypatch sys.argv instead of using an argument to main()

Just a style thing... didn't want to complicate the main func
for the sake of a couple tests

cibuildwheel/__main__.py

@@ -2,7 +2,7 @@ import argparse
 import os
 import sys
 import textwrap
-from typing import List, Optional, Set, Union
+from typing import List, Set, Union
 
 import cibuildwheel
 import cibuildwheel.linux
@@ -15,7 +15,7 @@ from cibuildwheel.typing import PLATFORMS, PlatformName, assert_never
 from cibuildwheel.util import BuildSelector, Unbuffered, detect_ci_provider
 
 
-def main(sys_args: Optional[List[str]] = None) -> None:
+def main() -> None:
     platform: PlatformName
 
     parser = argparse.ArgumentParser(
@@ -98,7 +98,7 @@ def main(sys_args: Optional[List[str]] = None) -> None:
         help="Enable pre-release Python versions if available.",
     )
 
-    args = parser.parse_args(args=sys_args, namespace=CommandLineArguments())
+    args = parser.parse_args(namespace=CommandLineArguments())
 
     if args.platform != "auto":
         platform = args.platform

unit_test/option_prepare_test.py

@@ -1,5 +1,6 @@
 import platform as platform_module
 import subprocess
+import sys
 from contextlib import contextmanager
 from pathlib import Path
 from typing import cast
@@ -40,9 +41,11 @@ def mock_build_docker(monkeypatch):
     monkeypatch.setattr("cibuildwheel.util.print_new_wheels", ignore_context_call)
 
 
-def test_build_default_launches(mock_build_docker, fake_package_dir):
+def test_build_default_launches(mock_build_docker, fake_package_dir, monkeypatch):
+    monkeypatch.setattr(sys, "argv", ["cibuildwheel", "--platform=linux"])
+
+    main()
 
-    main(["--platform=linux"])
     build_on_docker = cast(mock.Mock, linux.build_on_docker)
 
     assert build_on_docker.call_count == 4
@@ -106,7 +109,10 @@ before-all = "true"
     )
 
     monkeypatch.chdir(pkg_dir)
-    main(["--platform=linux"])
+    monkeypatch.setattr(sys, "argv", ["cibuildwheel", "--platform=linux"])
+
+    main()
+
     build_on_docker = cast(mock.Mock, linux.build_on_docker)
 
     assert build_on_docker.call_count == 6