ci: temporarily remove iOS 16 from the test matrix

Tests iPhone and iPad 16 are currently failing.

Saucelabs error message:

> An unknown server-side error occurred while processing the command. Original error: W3C capabilities should be provided

It might be time to migrate from zuul (https://github.com/defunctzombie/zuul).

zuul.config.js

@@ -1,7 +1,5 @@
 'use strict';
 
-const browsers = require('socket.io-browsers');
-
 const webpackConfig = require('./support/prod.config.js');
 
 webpackConfig.module.rules.push({
@@ -47,5 +45,30 @@ if (process.env.CI === 'true') {
   };
 }
 
-const isPullRequest = process.env.TRAVIS_PULL_REQUEST && process.env.TRAVIS_PULL_REQUEST !== 'false';
-zuulConfig.browsers = isPullRequest ? browsers.pullRequest : browsers.all;
+zuulConfig.browsers = [
+  {
+    name: 'chrome',
+    version: 'latest'
+  }, {
+    name: 'firefox',
+    version: 'latest'
+  }, {
+    name: 'internet explorer',
+    version: '9..11'
+  }, {
+    name: 'safari',
+    version: 'latest'
+  }, {
+    name: 'iphone',
+    version: '15.4' // temporary fix
+  }, {
+    name: 'android',
+    version: '5.1..6.0'
+  }, {
+    name: 'ipad',
+    version: '15.4' // temporary fix
+  }, {
+    name: 'MicrosoftEdge',
+    version: 'latest'
+  }
+];