Update dependency @web/test-runner to v0.13.20 (#200)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

package-lock.json

@@ -32,7 +32,7 @@
     "@open-wc/testing": "3.0.1",
     "@snowpack/plugin-typescript": "1.2.1",
     "@web/dev-server-esbuild": "0.2.14",
-    "@web/test-runner": "0.13.18",
+    "@web/test-runner": "0.13.20",
     "@web/test-runner-puppeteer": "0.10.2",
     "snowpack": "3.8.8",
     "typescript": "4.4.3"