message: add the inverse `is_not has_installed_exe` assertion
diff: @@ -1050,6 +1050,7 @@ fn installs_from_cwd_with_2018_warnings() {
  or use --path or --git to specify alternate source\
  "),
  );
  + assert_that(cargo_home(), is_not(has_installed_exe("foo")));
  }
  #[test]
  