Fix errcheck issues in server/channels/app/plugin_reattach (#29115)

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

server/.golangci.yml

@@ -139,7 +139,6 @@ issues:
         channels/app/plugin_health_check_test.go|\
         channels/app/plugin_hooks_test.go|\
         channels/app/plugin_install.go|\
-        channels/app/plugin_reattach.go|\
         channels/app/plugin_requests.go|\
         channels/app/plugin_signature.go|\
         channels/app/plugin_signature_test.go|\