"dart run" breaks in subpath with outdated lock

[davidmorgan]

If you use dart run from the package root, it seems to notice if the pubspec lock is out of date and update it

dart run test # works
touch pubspec.yaml
dart run test # works

but if you run from a subdirectory, it fails

cd lib
dart run test
touch ../pubspec.yaml
dart run test
--> fails "Could not find a file named "pubspec.yaml" in "/tmp/build_benchmark/built_value_loop_1000/lib"."

(yes, I know "dart run test" is a weird thing to do, I'm just using "test" as something you can probably run; any "dart run" should do the same).