Op refs to directories missing an op.yml aren't caught as data resolution errors

[chrisdostert]

🐛 Bug Report

When I opctl run notAnOp and notAnOp is a valid directory but has no op.yml, I don't get a fancy error.

To Reproduce

1. Create a directory at ./.opspec/notAnOp
2. Run opctl run notAnOp

Expected behavior

fancy error:

unable to resolve op 'notAnOp': 
- filesystem: 
  - path [omitted]/.opspec/notAnOp/op.yml not found
  - path [omitted]/notAnOp/op.yml not found
- opctl node: unable to resolve op 'notAnOp': 
  - filesystem: skipped
  - git: invalid git ref: missing version

Actual Behavior

open /Users/chrisdostert/repos/github.com/opctl/opctl/cli/.opspec/test/op.yml: no such file or directory

[chrisdostert]

@apexskier maybe you'd be interested/willing to take on