Pass file handle to ContainerIO

[radarhere]

This is part of #8362 - I'm hoping to break down that PR into easier-to-review chunks.

#7656 set ContainerIO to receive IO as the type of the first argument.

Pillow/src/PIL/ContainerIO.py

Line 29 in f9767fb

def __init__(self, file: IO[AnyStr], offset: int, length: int) -> None:

Currently, test_file_container.py passes an image instance to it sometimes - the wrong type.

Pillow/Tests/test_file_container.py

Lines 18 to 19 in f9767fb

	with hopper() as im:
	container = ContainerIO.ContainerIO(im, 0, 0)

This PR fixes that, passing a file handle to it like the rest of the test file does.

Pillow/Tests/test_file_container.py

Lines 41 to 42 in f9767fb

	with open(TEST_FILE, "rb") as fh:
	container = ContainerIO.ContainerIO(fh, 22, 100)