Tell pytest-playwright to run Chrome with --disable-web-security for end-to-end testing

conftest.py

@pytest.fixture(scope="session")
def browser(launch_browser):
    browser = launch_browser(
        # Tell playwright to disable CORS etc. in Chrome, so our webpack
        # dev-server domain can talk to our pytest live_server.url API
        # domain.
        args=["--disable-web-security"],
    )
    yield browser
    browser.close()