chore: upgrade @web/test-runner and increase timeout (#6870)

We've seen the odd timeout on the bots; increasing this in the hope that
it helps stop the flakes.

package.json

@@ -82,7 +82,7 @@
     "@types/ws": "^7.2.4",
     "@typescript-eslint/eslint-plugin": "^4.4.0",
     "@typescript-eslint/parser": "^4.4.0",
-    "@web/test-runner": "^0.9.2",
+    "@web/test-runner": "^0.12.15",
     "commonmark": "^0.28.1",
     "cross-env": "^7.0.2",
     "eslint": "^7.10.0",

web-test-runner.config.js

@@ -17,6 +17,7 @@ const { chromeLauncher } = require('@web/test-runner-chrome');
 
 module.exports = {
   files: ['test-browser/**/*.spec.js'],
+  browserStartTimeout: 60 * 1000,
   browsers: [
     chromeLauncher({
       async createPage({ browser }) {