[FIX] hr: hide new contract button if there is no contract dates

This hides the New Contract button when there are no contracts associated with the employee.

Task: 5231904

Author: HashemKhaled

addons/hr/views/hr_employee_views.xml

@@ -370,7 +370,7 @@
                                             <span invisible="not contract_date_start">to</span>
                                             <field name="contract_date_end" string="End Date" placeholder="Indefinite"
                                                 class="o_hr_narrow_field ms-3" invisible="not contract_date_start"/>
-                                            <widget name="button_new_contract"/>
+                                            <widget name="button_new_contract" invisible="not contract_date_start"/>
                                         </div>
                                         <label for="wage"/>
                                         <div class="o_row" name="wage">