Update dependency @web/test-runner to ^0.20.0 (#22)

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

Author: renovate[bot]

package-lock.json

@@ -34,7 +34,7 @@
     "@typescript-eslint/eslint-plugin": "^8.20.0",
     "@typescript-eslint/parser": "^8.20.0",
     "@web/dev-server": "^0.4.6",
-    "@web/test-runner": "^0.19.0",
+    "@web/test-runner": "^0.20.0",
     "concurrently": "^9.1.2",
     "eslint": "^9.18.0",
     "eslint-config-prettier": "^10.0.1",