Update dependency sinon to v21

Author: renovate[bot]

package-lock.json

@@ -47,7 +47,7 @@
     "madge": "^8.0.0",
     "prettier": "^3.4.2",
     "rimraf": "^6.0.1",
-    "sinon": "^20.0.0",
+    "sinon": "^21.0.0",
     "ts-lit-plugin": "^2.0.2",
     "tslib": "^2.8.1",
     "typescript": "^5.8.2",