Fix errcheck issues in server/channels/app/plugin_deadlock_test.go (#29113)

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

server/.golangci.yml

@@ -133,7 +133,6 @@ issues:
         channels/app/plugin_api_tests/manual.test_http_hijack_plugin/main.go|\
         channels/app/plugin_api_tests/manual.test_serve_metrics_plugin/main.go|\
         channels/app/plugin_api_tests/test_update_user_auth_plugin/main.go|\
-        channels/app/plugin_deadlock_test.go|\
         channels/app/plugin_health_check_test.go|\
         channels/app/plugin_install.go|\
         channels/app/plugin_requests.go|\

server/channels/app/plugin_deadlock_test.go

@@ -82,7 +82,8 @@ func TestPluginDeadlock(t *testing.T) {
 		}
 		for _, pluginTemplate := range pluginTemplates {
 			b := &strings.Builder{}
-			pluginTemplate.Execute(b, templateData)
+			err := pluginTemplate.Execute(b, templateData)
+			require.NoError(t, err)
 
 			plugins = append(plugins, b.String())
 		}
@@ -189,7 +190,8 @@ func TestPluginDeadlock(t *testing.T) {
 		}
 		for _, pluginTemplate := range pluginTemplates {
 			b := &strings.Builder{}
-			pluginTemplate.Execute(b, templateData)
+			err := pluginTemplate.Execute(b, templateData)
+			require.NoError(t, err)
 
 			plugins = append(plugins, b.String())
 		}
@@ -272,7 +274,8 @@ func TestPluginDeadlock(t *testing.T) {
 		}
 		for _, pluginTemplate := range pluginTemplates {
 			b := &strings.Builder{}
-			pluginTemplate.Execute(b, templateData)
+			err := pluginTemplate.Execute(b, templateData)
+			require.NoError(t, err)
 
 			plugins = append(plugins, b.String())
 		}