Update dependency @open-wc/testing to v3.1.6

Author: renovate[bot]

package-lock.json

@@ -29,7 +29,7 @@
     "tslib": "2.3.1"
   },
   "devDependencies": {
-    "@open-wc/testing": "3.0.1",
+    "@open-wc/testing": "3.1.6",
     "@snowpack/plugin-typescript": "1.2.1",
     "@web/dev-server-esbuild": "0.2.14",
     "@web/test-runner": "0.13.20",