fix: plugin test errcheck issues (#28531)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/.golangci.yml

@@ -83,7 +83,6 @@ issues:
         channels/api4/license_local.go|\
         channels/api4/oauth_test.go|\
         channels/api4/plugin.go|\
-        channels/api4/plugin_test.go|\
         channels/api4/post_test.go|\
         channels/api4/preference_test.go|\
         channels/api4/reaction_test.go|\