fix: remove extra "p"

Author: shenyih0ng

docs/source/generics.rst

@@ -146,7 +146,7 @@ example (Python 3.12 syntax):
    from typing import Mapping, Iterator
 
    # This is a generic subclass of Mapping
-   class MyMapp[KT, VT](Mapping[KT, VT]):
+   class MyMap[KT, VT](Mapping[KT, VT]):
        def __getitem__(self, k: KT) -> VT: ...
        def __iter__(self) -> Iterator[KT]: ...
        def __len__(self) -> int: ...