Bump kotlin to v1.7.20

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.jetbrains.kotlin.plugin.serialization (source)	1.7.10 -> 1.7.20
org.jetbrains.kotlin.multiplatform (source)	1.7.10 -> 1.7.20
org.jetbrains.kotlin.jvm (source)	1.7.10 -> 1.7.20
org.jetbrains.kotlin:kotlin-serialization (source)	1.7.10 -> 1.7.20
org.jetbrains.kotlin:kotlin-test (source)	1.7.10 -> 1.7.20
org.jetbrains.kotlin:kotlin-gradle-plugin (source)	1.7.10 -> 1.7.20

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