Pydantic Union with SkipJsonSchema breaks schema generation

[mskrip]

Describe the Bug

When using SkipJsonSchema annotation in a type union, the schema generation fails with Type str cannot be used in a GraphQL Union

Minimal replicating example:

import strawberry
from pydantic import BaseModel
from pydantic.json_schema import SkipJsonSchema


class ModelA(BaseModel):
    field_a: str | SkipJsonSchema[None] = None


@strawberry.experimental.pydantic.type(
    model=ModelA,
    all_fields=True,
)
class TypeA:
    pass


@strawberry.type
class Query:
    @strawberry.field
    def example(self) -> TypeA:
        return TypeA()


schema = strawberry.Schema(query=Query)
print(schema.as_str())

This pattern is useful for denoting the field as not required but without explicit type: none in JSON schema generated from Pydantic

System Information

• Operating system: Ubuntu
• Python version: 3.13
• Strawberry version (if applicable): 0.282.0