Two accounts with the same email

[pdpinch]

Steps to Reproduce

1. Enter an email, with lowercase letters in the address, at https://rc.xpro.mit.edu/create-account/
2. In another tab, open https://rc.xpro.mit.edu/create-account/ again and enter the same email, but all uppercase
3. You should get two verification emails, with different links.
4. Follow one of the links and complete the first screen of the account creation process
5. In a private window or another browser open the 2nd verification link and complete the first screen of the account creation process

Expected Behavior

• you should get an error when filling out the second form, because an account with that email already exists

Actual Behavior

• two accounts are created
• You can see where I've done this at https://rc.xpro.mit.edu/admin/users/user/?q=2024-04-24
• this happened in production to a user: https://github.com/mitodl/hq/issues/1274

[pdpinch]

I'm still checking whether this bug also exists on MITx Online