Merge pull request #185 from yiisoft/form-model-interface-has-attribute

* Fix Psalm - FormModelInterface::hasAttribute().

src/FormModelInterface.php

@@ -28,6 +28,15 @@ public function attributes(): array;
      */
     public function getAttributeValue(string $attribute);
 
+    /**
+     * If there is such attribute in the set.
+     *
+     * @param string $attribute
+     *
+     * @return bool
+     */
+    public function hasAttribute(string $attribute): bool;
+
     /**
      * @return FormErrorsInterface Validation errors.
      */