[FIX] proofreadpage_tests: Prepare redlink tests
[FIX] proofreadpage_tests: Prepare redlink tests

The test for redlinks in an index page have been added in f77fb56f but they
were using `dict.values` which is not stable and thus might change the order.
Additionally this is preparing the test class by creating the page instances
once.

Change-Id: I55084049460f39a27e36ff9b0f6a3e544db68d04

npdoty/pywikibot,jayvdb/pywikibot-core,Darkdadaah/pywikibot-core,darthbhyrava/pywikibot-local,magul/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,hasteur/g13bot_tools_new,hasteur/g13bot_tools_new,jayvdb/pywikibot-core,wikimedia/pywikibot-core,h4ck3rm1k3/pywikibot-core,happy5214/pywikibot-core,hasteur/g13bot_tools_new,h4ck3rm1k3/pywikibot-core,npdoty/pywikibot,Darkdadaah/pywikibot-core,magul/pywikibot-core,smalyshev/pywikibot-core,happy5214/pywikibot-core