fix: use precise type hint Optional[dict[str, Any]] for arguments parameter

- Update arguments parameter type hint from Optional[dict] to Optional[dict[str, Any]] in workflow_mixin.py
- Ensures consistency with BaseTool and improves static analysis and code clarity
- No functional changes, only type annotation improvement

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

tools/workflow/workflow_mixin.py

@@ -118,7 +118,7 @@ class BaseWorkflowMixin(ABC):
         max_tokens: Optional[int] = None,
         reserve_tokens: int = 1_000,
         remaining_budget: Optional[int] = None,
-        arguments: Optional[dict] = None,
+        arguments: Optional[dict[str, Any]] = None,
         model_context: Optional[Any] = None,
     ) -> tuple[str, list[str]]:
         """Prepare file content for prompts. Usually provided by BaseTool."""