esm: mark importAssertions as required

We already always specify a value, and failing to do so would likely be
a bug.

PR-URL: #46164
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/modules/esm/loader.js

@@ -777,14 +777,14 @@ class ESMLoader {
    * @param {string} originalSpecifier The specified URL path of the module to
    *                                   be resolved.
    * @param {string} [parentURL] The URL path of the module's parent.
-   * @param {ImportAssertions} [importAssertions] Assertions from the import
+   * @param {ImportAssertions} importAssertions Assertions from the import
    *                                              statement or expression.
    * @returns {{ format: string, url: URL['href'] }}
    */
   async resolve(
     originalSpecifier,
     parentURL,
-    importAssertions = { __proto__: null },
+    importAssertions,
   ) {
     const isMain = parentURL === undefined;