message: test: fix to error message for multitarget
diff: @@ -30,7 +30,7 @@ fn double_target_rejected_with_config() {
  .build();
  p.cargo("build")
  - .with_stderr("[ERROR] specifying multiple `--target` flags requires `-Zmultitarget`")
  + .with_stderr("[ERROR] specifying multiple `target` in `build.target` config value requires `-Zmultitarget`")
  .with_status(101)
  .run();
  }
  