[FIX] web: renderToElement should be detached

Before this commit, the element returned by the function
renderToElement, it was still attached to the parent <div> added in the
render function.

Now, the element returned is detached.

Part of task~3443861

Part-of: odoo/odoo#130467

addons/web/static/src/core/utils/render.js

@@ -3,7 +3,9 @@
 import { blockDom, markup } from "@odoo/owl";
 
 export function renderToElement(template, context = {}) {
-    return render(template, context).firstElementChild;
+    const el = render(template, context).firstElementChild;
+    el?.remove();
+    return el;
 }
 
 export function renderToFragment(template, context = {}) {

addons/web/static/tests/core/utils/render_tests.js

@@ -16,6 +16,11 @@ QUnit.module("utils", () => {
             </t>`
         );
         const compiledTemplate = renderToElement("test.render.template.1");
+        assert.strictEqual(
+            compiledTemplate.parentElement,
+            null,
+            "compiledTemplate.parentElement must be empty"
+        );
         assert.strictEqual(
             compiledTemplate.nodeType,
             Node.ELEMENT_NODE,