Merge pull request #1996 from nextcloud/renovate/kotlin-monorepo

fix(deps): update kotlin monorepo to v2.3.21

Author: AndyScherzinger

build.gradle

@@ -12,7 +12,7 @@
 
 buildscript {
     ext {
-        kotlin_version = '2.3.20'
+        kotlin_version = '2.3.21'
         jacoco_version = '0.8.14'
     }
 }