Bump kotlin_version from 1.5.0 to 1.5.20

Bumps `kotlin_version` from 1.5.0 to 1.5.20.

Updates `kotlin-gradle-plugin` from 1.5.0 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](https://github.com/JetBrains/kotlin/compare/v1.5.0...v1.5.20)

Updates `kotlin-stdlib-jdk7` from 1.5.0 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](https://github.com/JetBrains/kotlin/compare/v1.5.0...v1.5.20

)

Signed-off-by: dependabot[bot] <support@github.com>
Change-Id: Ibb5f2f9d674578b46db30b2ca5f0569f10dfd4f0