Update kotlin monorepo to v2.1.21 (#291)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

build.gradle

@@ -5,7 +5,7 @@ import com.android.build.gradle.BaseExtension
 import com.android.build.gradle.internal.CompileOptions
 
 buildscript {
-    ext.kotlin_version = '2.1.20'
+    ext.kotlin_version = '2.1.21'
     repositories {
         google()
         jcenter()