Bump kotlin-gradle-plugin from 1.5.10 to 1.5.21

Bumps kotlin-gradle-plugin from 1.5.10 to 1.5.21.

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -24,7 +24,7 @@
 buildscript {
 
     ext {
-        kotlinVersion = '1.5.10'
+        kotlinVersion = '1.5.21'
     }
 
     repositories {