[FIX] payment_paypal: Less confusing transaction logs

Before this commit, the log displayed "set as done"
before actually trying to put the transaction in done.
If an error then occurred in the'_set_transaction_done'
function and the transaction could not be processed,
this could lead to a misinterpretation of these logs.

This log is therefore moved after the transaction is
processed and is only displayed if it is actually successful.

This is valid for'done','pending' and'cancel'.

closes odoo/odoo#42078

X-original-commit: dd7552b1
Signed-off-by: jev <jev-odoo@users.noreply.github.com>