Only accept missing tkinter when building wheels on Windows

[radarhere]

Pillow/Tests/check_wheel.py

Lines 14 to 20 in 5a04b95

	# tkinter is not available in cibuildwheel installed CPython on Windows
	try:
	import tkinter
	assert tkinter
	except ImportError:
	expected_modules.remove("tkinter")

Let's increase the specificity of this code to only silently catch the error on Windows, as per the comment.

Since this PR hasn't actually triggered a Wheels job, I'll point to https://github.com/radarhere/Pillow/actions/runs/15235083611 as evidence that this does still pass.