[FIX] runbot: fix backend team errors tab visibility

Author: d-fence

runbot/views/dashboard_views.xml

@@ -25,7 +25,7 @@
                     </list>
                   </field>
                 </page>
-                <page string="Errors" invisible="bool(assignment_ids)">
+                <page string="Errors" invisible="not assignment_ids">
                   <field name="assignment_ids" nolabel="1" widget="many2many" options="{'not_delete': True, 'no_create': True}"/>
                 </page>
                 <page string="Modules">