Test suite: always test the Unsafe Browser in Farsi

It's a known-special case, due to advertising the homepage to be RTL, while
actually having English text (until those strings are actually translated),
which results in weird behavior. Better ensure our test suite always exercises
this case, rather than see the occasional seemingly random test failure, that
cannot be triaged without looking at the debug log.

features/step_definitions/unsafe_browser.rb

@@ -30,10 +30,10 @@ end
 Then /^the Unsafe Browser works in all supported languages$/ do
   failed = []
   # We always want the locale which we verify the startup page warning
-  # for ...
-  languages = ['fr_FR.UTF-8']
-  # ... then we just pick two *other* random locales.
-  languages += (supported_torbrowser_languages - languages).sample(2)
+  # for, and one RTL locale ...
+  languages = ['fr_FR.UTF-8', 'fa_IR.UTF-8']
+  # ... then we just pick one *other* random locale.
+  languages += (supported_torbrowser_languages - languages).sample(1)
   languages.each do |lang|
     step "I start the Unsafe Browser in the \"#{lang}\" locale"
     begin