Fix XML validation value type of post-code to "boolean"

Author: adragus-inviqa

app/code/Magento/Checkout/view/frontend/layout/checkout_index_index.xml

@@ -209,7 +209,7 @@
                                                                         <!-- post-code field has custom UI component -->
                                                                         <item name="component" xsi:type="string">Magento_Ui/js/form/element/post-code</item>
                                                                         <item name="validation" xsi:type="array">
-                                                                            <item name="required-entry" xsi:type="string">true</item>
+                                                                            <item name="required-entry" xsi:type="boolean">true</item>
                                                                         </item>
                                                                     </item>
                                                                     <item name="company" xsi:type="array">