fix(minor): adjust _SchemaConfig class to use literal values and not pydantic.config.Extra

[sfc-gh-twhite]

When running the tests, we're getting a few deprecation warnings. This one seems like low-hanging fruit.

agent_gateway/tools/base.py:58
orchestration-framework/agent_gateway/tools/base.py:58: PydanticDeprecatedSince20: `pydantic.config.Extra` is deprecated, use literal values instead (e.g. `extra='allow'`). Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.10/migration/
    extra: Any = Extra.forbid

This is where it's raising the deprecation warning at:

orchestration-framework/agent_gateway/tools/base.py

Lines 55 to 59 in 22c500b

	class _SchemaConfig:
	"""Configuration for the pydantic model."""
	extra: Any = Extra.forbid
	arbitrary_types_allowed: bool = True

[sfc-gh-twhite]

I think that this needs to become:

class _SchemaConfig:
    """Configuration for the pydantic model."""

    extra: str = "forbid"
    arbitrary_types_allowed: bool = True