tox.ini: Ignore N802 errors using per-file-ignores, not globally
tox.ini: Ignore N802 errors using per-file-ignores, not globally

This will help in gradually fixing them and prevents adding new ones
in files that don't have them already.

Change-Id: I59116ae68ddee27442ec3183d1386d7e477c89fa

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