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|\

server/channels/app/plugin_reattach.go

@@ -20,7 +20,10 @@ func (ch *Channels) ReattachPlugin(manifest *model.Manifest, pluginReattachConfi
 		return model.NewAppError("ReattachPlugin", "app.plugin.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}
 
-	ch.DetachPlugin(manifest.Id)
+	appErr := ch.DetachPlugin(manifest.Id)
+	if appErr != nil {
+		return appErr
+	}
 
 	// Reattach to the plugin
 	if err := pluginsEnvironment.Reattach(manifest, pluginReattachConfig); err != nil {