fix: input name overriding form method and action checks (#8471)

* change form.method to form.getAttribute

* add changeset

* normalise form.getAttribute value

* remove helper method and use HTMLFormElement.prototype

* change form.action to use HTMLFormElement.prototype

* revert unneccesary form cloning from runtime/client.js

* tidy up

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

.changeset/tidy-plants-relate.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: avoid input name clobbering form method check

packages/kit/src/runtime/app/forms.js

@@ -26,7 +26,11 @@ export function deserialize(result) {
 
 /** @type {import('$app/forms').enhance} */
 export function enhance(form, submit = () => {}) {
-	if (DEV && form.method !== 'post') {
+	if (
+		DEV &&
+		/** @type {HTMLFormElement} */ (HTMLFormElement.prototype.cloneNode.call(form)).method !==
+			'post'
+	) {
 		throw new Error('use:enhance can only be used on <form> fields with method="POST"');
 	}