gh-99535: Add test for inheritance of annotations and update documentation

Doc/howto/annotations.rst

@@ -57,6 +57,10 @@ Accessing The Annotations Dict Of An Object In Python 3.10 And Newer
   newer is to call :func:`getattr` with three arguments,
   for example ``getattr(o, '__annotations__', None)``.
 
+  Starting from Python 3.10, accessing the annotations
+  of a class will not give anymore the ones of its base
+  classes.
+
 
 Accessing The Annotations Dict Of An Object In Python 3.9 And Older
 ===================================================================

Lib/test/test_grammar.py

@@ -415,6 +415,19 @@ class Cbad2(C):
                 x: int
                 x.y: list = []
 
+    def test_annotations_inheritance(self):
+        # Check that annotations are not inherited by derived classes
+        class A:
+            attr: int
+        class B(A):
+            pass
+        class C(A):
+            attr: str
+        self.assertEqual(A.__annotations__, {"attr": int})
+        self.assertEqual(B.__annotations__, {})
+        self.assertEqual(C.__annotations__, {"attr" : str})
+
+
     def test_var_annot_metaclass_semantics(self):
         class CMeta(type):
             @classmethod