Update dependency org.jetbrains.kotlin:kotlin-gradle-plugin to v1.5.21

Author: renovate-bot

build.gradle

@@ -1,6 +1,6 @@
 buildscript {
     ext{
-        kotlin_version = '1.5.20'
+        kotlin_version = '1.5.21'
         nav_version = "2.4.0-alpha04"
     }