[IMP] hr_holidays: make const with working 8h per day
[IMP] hr_holidays: make const with working 8h per day

Having the number 8 in the code makes developers wonder 'why this number ?'. Naming it eases tensions in geek's mind.

ygol/odoo,hip-odoo/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,ygol/odoo,dfang/odoo,ygol/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo