docs: runnable docstring space (#25106)

libs/core/langchain_core/runnables/base.py

@@ -108,8 +108,8 @@ Other = TypeVar("Other")
 class Runnable(Generic[Input, Output], ABC):
     """A unit of work that can be invoked, batched, streamed, transformed and composed.
 
-     Key Methods
-     ===========
+    Key Methods
+    ===========
 
     - **invoke/ainvoke**: Transforms a single input into an output.
     - **batch/abatch**: Efficiently transforms multiple inputs into outputs.