Update eslint monorepo to v9.21.0 (#1111)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -37,7 +37,7 @@
     "@embroider/compat": "3.8.3",
     "@embroider/core": "3.5.2",
     "@embroider/webpack": "4.1.0",
-    "@eslint/js": "9.19.0",
+    "@eslint/js": "9.21.0",
     "@glimmer/component": "1.1.2",
     "@glimmer/tracking": "1.1.2",
     "@glint/core": "1.5.2",
@@ -90,7 +90,7 @@
     "ember-template-lint-plugin-prettier": "5.0.0",
     "ember-test-selectors": "7.0.0",
     "ember-truth-helpers": "4.0.3",
-    "eslint": "9.19.0",
+    "eslint": "9.21.0",
     "eslint-config-prettier": "10.0.2",
     "eslint-plugin-ember": "12.5.0",
     "eslint-plugin-n": "17.16.2",