[bugfix] Use current_page.site instead of self.site
[bugfix] Use current_page.site instead of self.site

With MultipleSitesBot self.site shouldn't be used. Page.site is
required instead.

Bug: T244962
Change-Id: If74897cd2e0bf176703017664074335eb20b9493

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core