Before this rev., we searched for 'label' tagname into the DOM, but
the fields labels are not always inside <label> (sometimes <span>).
However, they always have className 'o_form_label', so we use this
instead.
task 1961427
closesodoo/odoo#33487
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>