[FIX] account: cash based taxes mixed with regular ones

Previously, the use case where a cash basis tax and a regular one were combined on the same invoice line (for example) was not supported (technically, there's a single boolean for the tax exigibility of the sale/purchase line). Since it appears this is a real need, this have been improved in the generic tax report (in enterprise repo) in revision https://github.com/odoo/enterprise/commit/f7e33b8114d4d649551a155d0ca8cc4f43f1fc01 and this commit fixes the community side, to copy only the base line of the tax exigibile on payments in the cash basis move