mypy fix (pandas-dev#43356)

Co-authored-by: JHM Darbyshire (iMac) <[email protected]>

Author: attack68

pandas/io/formats/style.py

@@ -231,7 +231,7 @@ def __init__(
             thousands=thousands,
         )
 
-    def _repr_html_(self) -> str:
+    def _repr_html_(self) -> str | None:
         """
         Hooks into Jupyter notebook rich display system, which calls _repr_html_ by
         default if an object is returned at the end of a cell.
@@ -240,7 +240,7 @@ def _repr_html_(self) -> str:
             return self.to_html()
         return None
 
-    def _repr_latex_(self) -> str:
+    def _repr_latex_(self) -> str | None:
         if get_option("styler.render.repr") == "latex":
             return self.to_latex()
         return None