fix(config): Fixes SequentialAgent.config_type type hint

Without ClassVar, it will cause pydantic to generate warning.

PiperOrigin-RevId: 795518646

Author: Jacksunwei

src/google/adk/agents/llm_agent.py

@@ -130,7 +130,7 @@ class LlmAgent(BaseAgent):
   When not set, the agent will inherit the model from its ancestor.
   """
 
-  config_type: ClassVar[type[BaseAgentConfig]] = LlmAgentConfig
+  config_type: ClassVar[Type[BaseAgentConfig]] = LlmAgentConfig
   """The config type for this agent."""
 
   instruction: Union[str, InstructionProvider] = ''

src/google/adk/agents/sequential_agent.py

@@ -17,6 +17,7 @@
 from __future__ import annotations
 
 from typing import AsyncGenerator
+from typing import ClassVar
 from typing import Type
 
 from typing_extensions import override
@@ -33,7 +34,7 @@
 class SequentialAgent(BaseAgent):
   """A shell agent that runs its sub-agents in sequence."""
 
-  config_type: Type[BaseAgentConfig] = SequentialAgentConfig
+  config_type: ClassVar[Type[BaseAgentConfig]] = SequentialAgentConfig
   """The config type for this agent."""
 
   @override