gh-87864: Use correct function definition syntax in the docs (GH-103312)

(cherry picked from commit 50b4b15984)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

Lib/abc.py

@@ -18,7 +18,7 @@ def abstractmethod(funcobj):
 
         class C(metaclass=ABCMeta):
             @abstractmethod
-            def my_abstract_method(self, ...):
+            def my_abstract_method(self, arg1, arg2, argN):
                 ...
     """
     funcobj.__isabstractmethod__ = True