userlib.User has an unblock method but it wasn't ported to core yet.
Related Gerrit Patches:
|pywikibot/core : master||Implement User.unblock()|
|Invalid||None||T72936 Important tasks to be solved (tracking)|
|Open||None||T57880 Functionality existing in compat but missing from core (tracking)|
|Resolved||Mpaa||T134339 Port User.unblock from compat|