TYP: Fix pad_or_backfill limit_area type (#53866)

Author: mroeschke

pandas/core/internals/blocks.py

@@ -1352,7 +1352,7 @@ def pad_or_backfill(
         inplace: bool = False,
         limit: int | None = None,
         limit_direction: Literal["forward", "backward", "both"] = "forward",
-        limit_area: str | None = None,
+        limit_area: Literal["inside", "outside"] | None = None,
         fill_value: Any | None = None,
         downcast: Literal["infer"] | None = None,
         using_cow: bool = False,