Add a password rules quirk for gocurb.com

[rmondello]

Resolves #723

Overall Checklist

• [x] I agree to the project's Developer Certificate of Origin
• [x] The top-level JSON objects are sorted alphabetically
• [x] There are no open pull requests for the same update

for password-rules.json

• [x] The given rule isn't particularly standard and obvious for password managers
• [x] Generated passwords have been tested from this rule using the Password Rules Validation Tool
• [x] Information has been included about the website's requirements (eg. screenshots, error messages, steps during experimentation, etc.)
• [x] The PR isn't documenting something that would be a common practice among password managers (e.g. minimal length of 6)

[Sameesunkaria]

Screenshot from the app for reference.