Updates changelog for v1.13.1 release

Author: LordHepipud

doc/31-Changelog.md

@@ -7,7 +7,7 @@ documentation before upgrading to a new release.
 
 Released closed milestones can be found on [GitHub](https://github.com/Icinga/icinga-powershell-plugins/milestones?state=closed).
 
-## 1.13.1 (tbd)
+## 1.13.1 (2025-05-08)
 
 [Issue and PRs](https://github.com/Icinga/icinga-powershell-plugins/milestone/21)