fix: don't constrain build-system.requires with our dependency-versions (#2583)

* Don't constrain build-system.requires with dependency-versions

* Remove setting of VIRTUALENV_PIP (it doesn't appear to have any effect)

* Alter tests to assert the versions in before_build, not setup.py

* Skip the util-test on linux

---------

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

cibuildwheel/platforms/windows.py

@@ -23,7 +23,7 @@ from ..util import resources
 from ..util.cmd import call, shell
 from ..util.file import CIBW_CACHE_PATH, copy_test_sources, download, extract_zip, move_file
 from ..util.helpers import prepare_command, unwrap
-from ..util.packaging import combine_constraints, find_compatible_wheel, get_pip_version
+from ..util.packaging import find_compatible_wheel, get_pip_version
 from ..venv import constraint_flags, find_uv, virtualenv
 
 
@@ -468,13 +468,6 @@ def build(options: Options, tmp_path: Path) -> None:
                     shell("graalpy -m pip install setuptools wheel", env=env)
                     extra_flags = [*extra_flags, "-n"]
 
-                build_env = env.copy()
-                if pip_version is not None:
-                    build_env["VIRTUALENV_PIP"] = pip_version
-
-                if constraints_path:
-                    combine_constraints(build_env, constraints_path, identifier_tmp_dir)
-
                 match build_frontend.name:
                     case "pip":
                         # Path.resolve() is needed. Without it pip wheel may try to fetch package from pypi.org
@@ -488,7 +481,7 @@ def build(options: Options, tmp_path: Path) -> None:
                             f"--wheel-dir={built_wheel_dir}",
                             "--no-deps",
                             *extra_flags,
-                            env=build_env,
+                            env=env,
                         )
                     case "build" | "build[uv]":
                         if (
@@ -506,7 +499,7 @@ def build(options: Options, tmp_path: Path) -> None:
                             "--wheel",
                             f"--outdir={built_wheel_dir}",
                             *extra_flags,
-                            env=build_env,
+                            env=env,
                         )
                     case _:
                         assert_never(build_frontend)