__unicode__ always returns str (#9248)

stubs/vobject/vobject/base.pyi

@@ -65,7 +65,7 @@ class ContentLine(VBase):
     def __setattr__(self, name: str, value) -> None: ...
     def __delattr__(self, name: str) -> None: ...
     def valueRepr(self): ...
-    def __unicode__(self): ...
+    def __unicode__(self) -> str: ...
     def prettyPrint(self, level: int = ..., tabwidth: int = ...) -> None: ...
 
 class Component(VBase):