Add @type_check_only to stub-only private classes in various third-party stubs (#15535)

stubs/qrcode/qrcode/_types.pyi

@@ -1,6 +1,6 @@
 # Type aliases used in this stub package
 from _typeshed import SupportsWrite
-from typing import Any, Protocol
+from typing import Any, Protocol, type_check_only
 from typing_extensions import TypeAlias
 
 Box: TypeAlias = tuple[tuple[int, int], tuple[int, int]]
@@ -11,5 +11,6 @@ Ink: TypeAlias = tuple[int, int, int] | tuple[int, int, int, int]
 ErrorCorrect: TypeAlias = int
 MaskPattern: TypeAlias = int
 
+@type_check_only
 class Writeable(SupportsWrite[bytes], Protocol):
     def seek(self, offset: int, /) -> Any: ...