[bugfix] Fix a bug in --registry_path handling (#1101)

A bug in the handling of `--registry_path` was introduced in
https://github.com/openai/evals/pull/1036/files#diff-a694333152a5a73db19b8951647e60aed78f43fec6b119707bc6d489289be6c0R87

To repro, run the example from
https://github.com/openai/evals/blob/main/examples/retrieval-completionfn.ipynb

Before the fix, the following exception will be thrown
```
TypeError: unsupported operand type(s) for /: 'list' and 'str'
```

Author: pgarbacki

evals/cli/oaieval.py

@@ -84,7 +84,7 @@ def run(args: OaiEvalArguments, registry: Optional[Registry] = None) -> str:
 
     registry = registry or Registry()
     if args.registry_path:
-        registry.add_registry_paths([args.registry_path])
+        registry.add_registry_paths(args.registry_path)
 
     eval_spec = registry.get_eval(args.eval)
     assert (