[FIX] event_crm: correctly update lead phone when created from registration

When having rules creating leads from registrations, email and phone are
copied from the registration if the linked partner has no value for those
fields. However an error in the code lead to setting phone into email which
is not really correct.

This commit also add tests for event_crm who allowed to spot other issues
which are fixed in the next commits.

Task-3431124

Part-of: odoo/odoo#128823