Merge pull request #1726 from nextcloud/renovate/kotlin-monorepo

fix(deps): update kotlin monorepo to v2.1.21

Author: AndyScherzinger

build.gradle

@@ -12,7 +12,7 @@
 
 buildscript {
     ext {
-        kotlin_version = '2.1.20'
+        kotlin_version = '2.1.21'
         jacoco_version = '0.8.13'
     }
 }