gha: webui: Disable web security in tests

Fixes webui tests on gha:
```
Testing test/all_tests.html
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
Access to XMLHttpRequest at 'file:///__w/freeipa/freeipa/install/ui/test/qunit.js' from origin 'null' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-untrusted, https.
Failed to load resource: net::ERR_FAILED
Access to XMLHttpRequest at 'file:///__w/freeipa/freeipa/install/ui/test/data/i18n_messages.json' from origin 'null' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-untrusted, https.
Failed to load resource: net::ERR_FAILED
>> Error: Error: Couldn't receive translations
```

See gruntjs/grunt-contrib-qunit#158 for details.

install/ui/Gruntfile.js

@@ -4,6 +4,15 @@ module.exports = function(grunt) {
  options: {}
  },
  qunit: {
+ options: {
+ puppeteer: {
+ ignoreDefaultArgs: true,
+ args: [
+ "--headless",
+ "--disable-web-security"
+ ]
+ },
+ },
  all: [
  'test/all_tests.html'
  ]