Quote HTTP response status keys in the generated OpenAPI YAML

[verdie-g]

defs/asana_oas.yaml emits HTTP response status keys as unquoted YAML numbers:

responses:
  200:
  400:
  401:

YAML parsers decode these keys as integers, but OpenAPI Response Object status-code keys are strings. Strict parsers such as openapi-pydantic reject the document; the current specification produces 1,542 validation errors for this reason.

Could the generator quote these keys?

responses:
  "200":
  "400":
  "401":

Stringifying the keys before validation makes the document pass.