test: Add unit tests for SignUpForm

The meethub/accounts/forms.py file contains the SignUpForm, but there are no tests for it in meethub/accounts/tests/test_forms.py. We need to add tests to ensure it validates data correctly and creates a user and profile upon saving

Acceptance Criteria:

1. Create meethub/accounts/tests/test_forms.py.
2. Add tests for valid form data.
3. Add tests for invalid data (e.g., mismatched passwords, existing email).
4. Test that the save() method correctly creates an Account and a Profile.