hr_payroll_cancel/hr_payslip_workflow.xml

<?xml version='1.0' encoding='UTF-8'?>
<openerp>
    <data>
        <record id="hr_payroll.act_done" model="workflow.activity">
            <field name="wkf_id" ref="hr_payroll.wkf"/>
            <field name="name">done</field>
            <field name="action">process_sheet()</field>
            <field name="kind">function</field>
            <field name="flow_stop"/>
        </record>
        
        <record id="workflow_transition_act_done_to_act_cancel" model="workflow.transition">
            <field name="signal">cancel_sheet</field>
            <field name="act_from" ref="hr_payroll.act_done"/>
            <field name="act_to" ref="hr_payroll.act_cancel"/>
            <field name="condition">True</field>
        </record>
        
    </data>
</openerp>