Fix flaky specs in identity verification feature specs

What does this MR do and why?

• Resolves gitlab-org/quality/engineering-productivity/master-broken-incidents#3691 (closed), #425460 (closed), #375306 (closed)
• We had two identity verification feature specs - /users/identity_verification_spec.rb and /registrations/identity_verification_spec.rb. I have consolidated them into one file
• The errors in the pipelines as evident from the artifacts was being caused because we were confirming the user with user.confirm and then requesting a new verification code.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.