Fix for #1677 (#1678)

* Make `as_markup` return `super().as_markup`

* Add 1677.misc.rst

* Update 1677.misc.rst

CHANGES/1677.misc.rst

@@ -0,0 +1,5 @@
+Fixed MyPy [return-value] error in `InlineKeyboardBuilder().as_markup()`.
+`as_markup` method now overloads parent class method and uses `super()`, to call parent's 
+`as_markup` method.
+Also added correct type hint to `as_markup`'s return in `InlineKeyboardBuilder` and 
+`ReplyKeyboardBuilder` classes.

aiogram/utils/keyboard.py

@@ -336,11 +336,9 @@ class InlineKeyboardBuilder(KeyboardBuilder[InlineKeyboardButton]):
             ),
         )
 
-    if TYPE_CHECKING:
-
-        def as_markup(self, **kwargs: Any) -> InlineKeyboardMarkup:
-            """Construct an InlineKeyboardMarkup"""
-            ...
+    def as_markup(self, **kwargs: Any) -> InlineKeyboardMarkup:
+        """Construct an InlineKeyboardMarkup"""
+        return cast(InlineKeyboardMarkup, super().as_markup(**kwargs))
 
     def __init__(self, markup: Optional[List[List[InlineKeyboardButton]]] = None) -> None:
         super().__init__(button_type=InlineKeyboardButton, markup=markup)
@@ -401,9 +399,9 @@ class ReplyKeyboardBuilder(KeyboardBuilder[KeyboardButton]):
             ),
         )
 
-    if TYPE_CHECKING:
-
-        def as_markup(self, **kwargs: Any) -> ReplyKeyboardMarkup: ...
+    def as_markup(self, **kwargs: Any) -> ReplyKeyboardMarkup:
+        """Construct a ReplyKeyboardMarkup"""
+        return cast(ReplyKeyboardMarkup, super().as_markup(**kwargs))
 
     def __init__(self, markup: Optional[List[List[KeyboardButton]]] = None) -> None:
         super().__init__(button_type=KeyboardButton, markup=markup)