message: Enable source_config_env test on Windows
diff: use cargo_test_support::{paths, project, registry::Package};
  #[cargo_test]
  -// I don't know why, but `Command` forces all env keys to be upper case on
  -// Windows. Seems questionable, since I think Windows is case-preserving.
  -#[cfg_attr(windows, ignore = "broken due to not preserving case on Windows")]
  fn source_config_env() {
  // Try to define [source] with environment variables.
  let p = project()
  