Bump kotlin-gradle-plugin from 1.5.10 to 1.5.20

Bumps [kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.5.10 to 1.5.20.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.5.20/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.5.10...v1.5.20)

---
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] <[email protected]>

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.5.10'
+    ext.kotlin_version = '1.5.20'
     repositories {
         google()
         jcenter()