Fix bug with ?plugin update. (modmail-dev#3295)

(cherry picked from commit a94e7a9)
Signed-off-by: Khakers <22665282+khakers@users.noreply.github.com>

Author: Jerrie-Aries

CHANGELOG.md

@@ -81,6 +81,7 @@ however, insignificant breaking changes do not guarantee a major version bump, s
 - Fixed blocked roles improperly saving in `blocked_users` config.
 - Fixed `?block` command improperly parsing reason as timestamp. 
 - Rate limit issue when fetch the messages due to reaction linking. ([PR #3306](https://github.com/modmail-dev/Modmail/pull/3306))
+- Update command fails when the plugin is invalid. ([PR #3295](https://github.com/modmail-dev/Modmail/pull/3295))
 
 ### Internal
 - `ConfigManager.get` no longer accepts two positional arguments: the `convert` argument is now keyword-only.

cogs/plugins.py

@@ -499,12 +499,12 @@ async def update_plugin(self, ctx, plugin_name):
                         description=f"Failed to update {plugin.name}. This plugin will now be removed from your bot.",
                         color=self.bot.error_color,
                     )
-                    self.bot.config["plugins"].remove(plugin_name)
-                    logger.debug("Failed to update %s. Removed plugin from config.", plugin_name)
+                    self.bot.config["plugins"].remove(str(plugin))
+                    logger.debug("Failed to update %s. Removed plugin from config.", plugin)
                 else:
-                    logger.debug("Updated %s.", plugin_name)
+                    logger.debug("Updated %s.", plugin)
             else:
-                logger.debug("Updated %s.", plugin_name)
+                logger.debug("Updated %s.", plugin)
             return await ctx.send(embed=embed)
 
     @plugins.command(name="update")