Generated code lacks import of typing.cast for required const properties

[benweint]

Describe the bug
When an input schema has a required const property, the generated code does makes calls to typing.cast, but does not import it, leading to failures when trying to run ruff over the generated code.

OpenAPI Spec File

openapi: 3.1.0
info:
  title: Pets Example
  version: 1.0.0
paths:
  /pets:
    post:
      requestBody:
        description: Create a new pet in the system
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Pet"
      responses:
        "200":
          description: Return a 200 status to indicate that the pet was created successfully

components:
  schemas:
    Pet:
      required:
        - type
      properties:
        type:
          const: cat

Desktop (please complete the following information):

• OS: macOS 14.6.1
• Python Version: 3.12.6
• openapi-python-client version: latest main (also present in latest release, 0.21.6)

Additional context

Removing type from the required field list in the example above makes the problem disappear - in this case, cast is still used, but is properly imported.