Tests: Make Karma browser timeout larger than the QUnit one

Since the default Karma browser no activity timeout was lower than the QUnit
timeout, a single timing out test was interrupting the whole test run of
a browser.

The QUnit timeout is set to 1 minute so I set the Karma one to 2 minutes.

Closes gh-4943

Gruntfile.js

@@ -232,6 +232,10 @@ module.exports = function( grunt ) {
 				],
 				reporters: [ "dots" ],
 				autoWatch: false,
+
+				// 2 minutes; has to be longer than QUnit.config.testTimeout
+				browserNoActivityTimeout: 120e3,
+
 				concurrency: 3,
 				captureTimeout: 20 * 1000,
 				singleRun: true