[Bug]: `_validate_reference` cannot resolve $ref with a relative file path

[chantera]

Actual Behavior

openapi.validate_response raises jsonschema.exceptions._WrappedReferencingError when the response schema defined in a different file includes $ref that refers to a schema in another file.

Expected Behavior

The validator should not raise the error for $ref.
I ensured no spec-related error occured when openapi.check_spec() called.

Steps to Reproduce

openapi.yaml

openapi: "3.0.0"
info:
 title: sample
 version: "0.1"
paths:
 /books:
 $ref: "./paths/books.yaml"

paths/books.yaml

get:
 responses:
 "200":
 description: OK
 content:
 application/json:
 schema:
 type: array
 items:
 $ref: "../schemas/book.yaml#/Book"

schemas/book.yaml

Book:
 type: object
 properties:
 id:
 $ref: "#/BookId"
 title:
 type: string
BookId:
 type: string

validate.py

import json
import os

import openapi_core
import openapi_core.testing

SPEC_PATH = os.path.join(os.path.dirname(__file__), "openapi.yaml")

openapi = openapi_core.OpenAPI.from_file_path(
 SPEC_PATH,
 config=openapi_core.Config(spec_base_uri=f"file://{SPEC_PATH}"),
)
openapi.check_spec() # ensure the spec is valid

request = openapi_core.testing.MockRequest(
 host_url="", method="GET", path="/books"
)
response = openapi_core.testing.MockResponse(
 data=json.dumps([{"id": "BOOK:01", "title": "Test Book"}]).encode()
)
openapi.validate_request(request)
openapi.validate_response(request, response) # raises error

Run:

$ python validate.py

OpenAPI Core Version

3.0.0,3.1.0

OpenAPI Core Integration

Nothing

Affected Area(s)

validation

References

No response

Anything else we need to know?

No response

Would you like to implement a fix?

Yes