schemas.openapi.SchemaGenerator.get_schema request argument should be optional

[dolfandringa]

The schemas.openapi.SchemaGenerator.get_schema request argument is optional in drf. If you override the clause, it either results in pyright complaining that we incorrectly override the method if we set the type of request: Request|None since the type is now different, or if we say request: Request = None of course it will show a type error, and if we leave out the default value, now we make it mandatory, while it shouldn't be.