ExifRead: Fix Reader.__iter__() (#12402)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: vinicius507

stubs/ExifRead/exifread/_types.pyi

@@ -1,5 +1,6 @@
 # Stubs-only module with type aliases for ExifRead.
 
+from collections.abc import Iterator
 from typing import Any, Literal, Protocol
 from typing_extensions import TypeAlias
 
@@ -8,7 +9,7 @@ from typing_extensions import TypeAlias
 TagDict: TypeAlias = dict[int, tuple[str] | tuple[str, Any]]
 
 class Reader(Protocol):
-    def __iter__(self) -> bytes: ...
+    def __iter__(self) -> Iterator[bytes]: ...
     def read(self, size: int, /) -> bytes: ...
     def tell(self) -> int: ...
     def seek(self, offset: int, whence: Literal[0, 1] = ..., /) -> object: ...