[boursorama] Corrected URLs for Loans

Loans are fetched on a loan detail page and the correponding account is
removed from the accounts_list, however it is crucial to add the loan
url for other methods in the module such as iter_transfer_recipients
that start with "assert account.url" and get_invest that starts with "if
/blabla/ in account.url".

Closes: 28577@sibi