adminchannel: allow non-op .topic in -t channels

Depends on sopel-irc#1980. Fixes sopel-irc#1842.

sopel/modules/adminchannel.py

@@ -308,16 +308,19 @@ def kickban(bot, trigger):
 
 
 @plugin.require_chanmsg
-@plugin.require_privilege(plugin.OP, ERROR_MESSAGE_NO_PRIV)
 @plugin.command('topic')
 def topic(bot, trigger):
     """Change the channel topic
 
-    The bot must be a channel operator for this command to work.
+    The bot must be a channel operator for this command to work in +t channels.
     """
-    if bot.channels[trigger.sender].privileges[bot.nick] < plugin.HALFOP:
+    mode_t = bot.channels[trigger.sender].modes.get("t", False)
+    if mode_t and bot.channels[trigger.sender].privileges[bot.nick] < plugin.HALFOP:
         bot.reply(ERROR_MESSAGE_NOT_OP)
         return
+    if mode_t and bot.channels[trigger.sender].privileges[trigger.nick] < plugin.HALFOP:
+        bot.reply(ERROR_MESSAGE_NO_PRIV)
+        return
     if not trigger.group(2):
         return
     channel = trigger.sender.lower()