Update coroutines to v1.6.4

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.jetbrains.kotlinx:kotlinx-coroutines-test	1.6.3 -> 1.6.4
org.jetbrains.kotlinx:kotlinx-coroutines-core	1.6.3 -> 1.6.4

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Release Notes

Kotlin/kotlinx.coroutines

v1.6.4

Compare Source

• Added TestScope.backgroundScope for launching coroutines that perform work in the background and need to be cancelled at the end of the test (#​3287).
• Fixed the POM of kotlinx-coroutines-debug having an incorrect reference to kotlinx-coroutines-bom, which cause the builds of Maven projects using the debug module to break (#​3334).
• Fixed the Publisher.await functions in kotlinx-coroutines-reactive not ensuring that the Subscriber methods are invoked serially (#​3360). Thank you, @​EgorKulbachka!
• Fixed a memory leak in withTimeout on K/N with the new memory model (#​3351).
• Added the guarantee that all Throwable implementations in the core library are serializable (#​3328).
• Moved the documentation to https://kotlinlang.org/api/kotlinx.coroutines/ (#​3342).
• Various documentation improvements.

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