[cleanup] pywikibot/site.py: simplify test
[cleanup] pywikibot/site.py: simplify test

The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).

Change-Id: I8ffa9da4f37b8851801e404e0c47ca6774dff828

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