docs: document Windows signing explicitly

Related to https://camunda.slack.com/archives/GP70M0J6M/p1741163415194969

docs/.project/RELEASE_TEMPLATE.md

@@ -63,6 +63,7 @@ _To be done to build the release after release testing completed._
 _To be done once the release is built._
 
 * [ ] communicate release with closed support-related issues to [#ask-support](https://camunda.slack.com/archives/CHAC0L80M) (automated)
+* [ ] make sure Windows artifacts are signed
 * [ ] publish release on [Github Releases](https://github.com/camunda/camunda-modeler/releases)
 * [ ] communicate the release to [support](https://app.slack.com/client/T0PM0P1SA/CHAC0L80M) (changelog link, closed support issues; [example message](https://camunda.slack.com/archives/CHAC0L80M/p1733480373630349))
 * [ ] close [current milestone](https://github.com/camunda/camunda-modeler/milestones)