Commit 4d64e553b8 introduced an 'mt-3' in the address layout of the
external background layout to fix a problem related to the display of
phone numbers.
That fix introduced an error with the pingen external post service. It
requires the area where the destination address is printed to be blank,
due to the mt-3, the background image was visible instead of that blank
area.
As removing solely the mt-3 doesn't break the first problem and solve
the second, it is safe to remove it.
Before this commit, no message was logged to help finding out why the
test was failing.
The `requests.raise_for_status` method raises an error on both 400 and
500 status code. We don't want the test to break in case pingen screw
up their side so 500 errors are just logged. 400 errors still raise an
exception.
closesodoo/odoo#36504
Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>