message: Fix a test.
  Presumably, it should failed when it was first written, but Cargo does not do such validation yet.
diff: @@ -1196,6 +1196,7 @@ fn test_path_dependency_under_member() {
  [dependencies]
  foo = { path = "../foo" }
  + [workspace]
  "#)
  .file("ws/src/lib.rs", r"extern crate foo; pub fn f() { foo::f() }")
  .file("foo/Cargo.toml", r#"
  