Fix the https-everywhere test in Tor Browser testsuite
In the Tor Browser test suite, we have an https-everywhere test that is checking that the URL http://www.freedomboxfoundation.org/thanks/ is redirected to its https version when https-everywhere is enabled.
However https-everywhere rules have been updated to add
platform="mixedcontent" to this host, which make it disabled by default:
We should update the test to use an other URL for checking that https-everywhere is working.