Max just dug this up to calm your fears 😉
If Steam asks for your Credit Card Info Mar 26, 23:39 Taylor Sherman
There's a bug in the Create Account Wizard that will, if you do the right sequence, get you to the "Enter your Credit Card Information" screen. If you get here, it means you've not entered the Special Offer Key, which is necessary for the Beta test. Go back (or cancel and come back) and fill it in. The "Next" button will become "Finish", and if you've entered the right key, your account will be created.
If you *do* (or did) enter CC info, don't worry, it was never sent anywhere. It's merely a dumb page left over from before. However I'll repeat here that no part of this Beta will need a credit card, so don't fill that information in if anything/one asks for it.
Taylor Sherman being a Steam developer 😉