Merge pull request #10102 from nextcloud/dependabot/gradle/kotlin_version-1.6.21

Bump kotlin_version from 1.6.20 to 1.6.21

build.gradle

@@ -1,7 +1,7 @@
 buildscript {
     ext {
         jacoco_version = '0.8.8'
-        kotlin_version = '1.6.20'
+        kotlin_version = '1.6.21'
         androidxTestVersion = "1.4.0"
         daggerVersion = "2.41"
         markwonVersion = "4.6.2"