[FIX] l10n_mx: set the 16% taxes as the default

Set the default sale and purchase taxes for the mexican CoA.

Before introducing the IEPS taxes in commit
734e18eb, the default taxes were the 16%
IVA taxes (when loading the CoA, the default is simply the first
possible match with the lowest sequence). As the IEPS taxes now have the
lowest sequence, they are incorrectly selected as the defaults. This
commit fixes this.

task-3507155

closes odoo/odoo#135810

Signed-off-by: Laurent Smet (las) <las@odoo.com>