minor symfony#57565 [AssetMapper] Upgrade importmap polyfill (smnandre)

This PR was submitted for the 7.2 branch but it was merged into the 6.4 branch instead.

Discussion
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[AssetMapper] Upgrade importmap polyfill

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? |  no
| Issues        | Fix #
| License       | MIT

Not sure if we should backport this on 6.4 ?

Commits
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385d1e8 [AssetMapper] Upgrade importmap polyfill

Author: nicolas-grekas

src/Symfony/Component/AssetMapper/ImportMap/ImportMapRenderer.php

@@ -27,7 +27,9 @@
  */
 class ImportMapRenderer
 {
-    private const DEFAULT_ES_MODULE_SHIMS_POLYFILL_URL = 'https://ga.jspm.io/npm:[email protected]/dist/es-module-shims.js';
+    // https://generator.jspm.io/#S2NnYGAIzSvJLMlJTWEAAMYOgCAOAA
+    private const DEFAULT_ES_MODULE_SHIMS_POLYFILL_URL = 'https://ga.jspm.io/npm:[email protected]/dist/es-module-shims.js';
+    private const DEFAULT_ES_MODULE_SHIMS_POLYFILL_INTEGRITY = 'sha384-ie1x72Xck445i0j4SlNJ5W5iGeL3Dpa0zD48MZopgWsjNB/lt60SuG1iduZGNnJn';
 
     public function __construct(
         private readonly ImportMapGenerator $importMapGenerator,