fix: Pass the scope conditionally for OAuth2 Password Credentials

[nicolasnobelis]

The scope param is always passed (when according to the spec, it is optional).

The server responds with

{ "error": "invalid_scope", "error_description": "Invalid scopes: " }

Fixes: https://github.com/usebruno/bruno/issues/2446.

[pietrygamat]

The same is true for other oauth2 grant types. Perhaps it's worth updating different ones as well?

[helloanoop]

Merged!

Thanks for working on this @nicolasnobelis ! Thanks for the review @pietrygamat @lohxt1 !