[FIX] account_edi: change logger type to 'warning' when upload corrupt pdf

'PdfReadError Could not read malformed PDF file' log error is generated
when user upload a corrupted PDF file in an invoice.

This commit changes the logger exception to a warning to avoid an
unnecessary error in the log. 

sentry-4188965420

closes odoo/odoo#121617

Signed-off-by: Quentin De Paoli <qdp@odoo.com>