Fix compatibility with Kotlin MPP plugin

[donat]

The Kotlin team reported that Gradle 7.6 broke the Kotlin MPP plugin. The root cause is a change in an internal TestResultProcessor class that is used by the plugin.

This PR restores compatibility by reverting the changes to the TestResultProcessor. More specifically, merging this PR would result in the following changes over the Gradle versions:

• Gradle 7.5: TestResultProcessor.failure(Object id, Throwable failure)
• Gradle 7.6: TestResultProcessor.failure(Object id, TestFailure failure)
• Gradle 7.6.1: TestResultProcessor.failure(Object id, Throwable failure)

Also, to preserve functionality, this PR makes TestFailure a subclass of Throwable.

[donat]

@bot-gradle test RFM

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