stdlib: Add many missing dunder overrides (#7231)

stdlib/configparser.pyi

@@ -80,6 +80,7 @@ class RawConfigParser(_parser):
     def __setitem__(self, section: str, options: _section) -> None: ...
     def __delitem__(self, section: str) -> None: ...
     def __iter__(self) -> Iterator[str]: ...
+    def __contains__(self, key: object) -> bool: ...
     def defaults(self) -> _section: ...
     def sections(self) -> list[str]: ...
     def add_section(self, section: str) -> None: ...