Bump kotlin-gradle-plugin from 1.6.20 to 1.6.21

Bumps [kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.6.20 to 1.6.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

---
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.kts

@@ -5,7 +5,7 @@ buildscript {
     }
     dependencies {
         classpath("com.android.tools.build:gradle:7.1.3")
-        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.20")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.21")
     }
 }