Changed function because ReadOnly Class can not be used in PHP8.1

Author: DemiTrinos

…ck/System/Config/Form/Field/ReadOnly.php …stem/Config/Form/Field/ReadOnlyField.phpBlock/System/Config/Form/Field/ReadOnly.php renamed to Block/System/Config/Form/Field/ReadOnlyField.php Block/System/Config/Form/Field/ReadOnly.php renamed to Block/System/Config/Form/Field/ReadOnlyField.php

@@ -1,13 +1,13 @@
-<?php
-namespace Experius\Postcode\Block\System\Config\Form\Field;
-
-use Magento\Framework\Data\Form\Element\AbstractElement;
-
-class ReadOnly extends \Magento\Config\Block\System\Config\Form\Field
-{
-    protected function _getElementHtml(AbstractElement $element)
-    {
-        $element->setData('readonly', 1);
-        return $element->getElementHtml();
-    }
-}
+<?php
+namespace Experius\Postcode\Block\System\Config\Form\Field;
+
+use Magento\Framework\Data\Form\Element\AbstractElement;
+
+class ReadOnlyField extends \Magento\Config\Block\System\Config\Form\Field
+{
+    protected function _getElementHtml(AbstractElement $element)
+    {
+        $element->setData('readonly', 1);
+        return $element->getElementHtml();
+    }
+}

etc/adminhtml/system.xml

@@ -22,7 +22,7 @@
                 </field>
                 <field id="api_key_is_valid" showInDefault="1" showInStore="1" showInWebsite="1" sortOrder="40" translate="label" type="text">
                     <label>Api Key is valid</label>
-                    <frontend_model>Experius\Postcode\Block\System\Config\Form\Field\ReadOnly</frontend_model>
+                    <frontend_model>Experius\Postcode\Block\System\Config\Form\Field\ReadOnlyField</frontend_model>
                 </field>
                 <field id="api_key_checker" showInDefault="1" showInStore="1" showInWebsite="1" sortOrder="41" translate="label" type="button">
                     <button_label>Check Api Key</button_label>