Bump kotlin-gradle-plugin from 1.5.10 to 1.5.20

Bumps kotlin-gradle-plugin from 1.5.10 to 1.5.20.

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

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