Add TEST_ENVIRONMENT option and set PYTHONSAFEPATH=1 in the test env (#2388)

* Add TEST_ENVIRONMENT option and set PYTHONSAFEPATH=1 in the test env

Closes https://github.com/pypa/cibuildwheel/issues/2358

* Add toml docs examples

* Add TOML examples

* Use double-quotes for windows

cibuildwheel/platforms/pyodide.py

@@ -380,6 +380,12 @@ def build(options: Options, tmp_path: Path) -> None:
                 )
                 virtualenv_env["VIRTUAL_ENV"] = str(venv_dir)
 
+                virtualenv_env["PYTHONSAFEPATH"] = "1"
+
+                virtualenv_env = build_options.test_environment.as_dictionary(
+                    prev_environment=virtualenv_env
+                )
+
                 # check that we are using the Python from the virtual environment
                 call("which", "python", env=virtualenv_env)