Update dependency @web/test-runner to ^0.20.0

Author: renovate[bot]

package.json

@@ -32,7 +32,7 @@
     "@typescript-eslint/eslint-plugin": "^6.0.0",
     "@typescript-eslint/parser": "^6.0.0",
     "@web/dev-server": "^0.4.0",
-    "@web/test-runner": "^0.19.0",
+    "@web/test-runner": "^0.20.0",
     "concurrently": "^8.0.0",
     "eslint": "^8.18.0",
     "eslint-config-prettier": "^9.0.0",