Changed ContainerIO to subclass IO

[radarhere]

There is a mypy error on Tests/test_file_tar.py

Tests/test_file_tar.py:25: error: Argument 1 to "open" has incompatible type "TarIO"; expected "Union[Union[str, bytes, PathLike[str], PathLike[bytes]], IO[bytes]]" 
[arg-type]
                with Image.open(tar) as im:
                                ^~~
Found 1 error in 1 file (checked 1 source file)

Pillow/src/PIL/Image.py

Lines 3357 to 3358 in 86f4cfb

	def open(
	fp: StrOrBytesPath | IO[bytes],

doesn't accept TarIO, which subclasses from ContainerIO

Pillow/src/PIL/ContainerIO.py

Line 22 in 86f4cfb

class ContainerIO(Generic[AnyStr]):

I don't think there's any reason why ContainerIO shouldn't subclass IO - it is essentially performing that role - so I've made that change here.