--only doesn't work for -win32 identifiers

[joerick]

• cp311 https://github.com/ddelange/asyncpg/actions/runs/3092263953/jobs/5003341864#step:4:43
• same for all other win32 builds: Invalid --only='cp310-win32', must be a build selector with a known platform

in ddelange/asyncpg#2

and before this change it was fine: https://github.com/ddelange/asyncpg/actions/runs/3072698535/jobs/4964355341#step:4:89

maybe it's an issue with the --only flag?

on my mac:

$ cibuildwheel --print-build-identifiers --platform windows --arch x86,AMD64
cp36-win32
cp36-win_amd64
cp37-win32
cp37-win_amd64
cp38-win32
cp38-win_amd64
cp39-win32
cp39-win_amd64
cp310-win32
cp310-win_amd64
cp311-win32
cp311-win_amd64
pp37-win_amd64
pp38-win_amd64
pp39-win_amd64

Originally posted by @ddelange in #1266 (comment)

[joerick]

Issue seems to be this line:

https://github.com/mayeut/cibuildwheel/blob/6df5de717552b07dfee43760b154f0bf8a1af4ed/cibuildwheel/__main__.py#L176