Bump kotlinVersion from 1.5.20 to 1.5.21

Bumps `kotlinVersion` from 1.5.20 to 1.5.21.

Updates `kotlin-gradle-plugin` from 1.5.20 to 1.5.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.5.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.5.20...v1.5.21)

Updates `kotlin-stdlib-jdk8` from 1.5.20 to 1.5.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.5.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.5.20...v1.5.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build.gradle

@@ -1,6 +1,6 @@
 buildscript {
     ext {
-        kotlinVersion = '1.5.20'
+        kotlinVersion = '1.5.21'
         moshiVersion = "1.12.0"
     }