Fixed errcheck issues in server/channels/app/server.go (#29425)

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

server/.golangci.yml

@@ -100,7 +100,6 @@ issues:
         channels/app/plugin_test.go|\
         channels/app/post_helpers_test.go|\
         channels/app/post_test.go|\
-        channels/app/server.go|\
         channels/app/slack.go|\
         channels/app/slashcommands/auto_environment.go|\
         channels/app/slashcommands/command_test.go|\