Fix TestScope factory KDoc formatting

[PhilGlass]

The docs for the TestScope factory function are supposed to include a nested list, but the indentation is wrong so the KDoc is a bit confusing.

Before:

After:

[dkhalanskyjb]

Thanks! Could you target the master branch instead? From https://github.com/Kotlin/kotlinx.coroutines/blob/master/CONTRIBUTING.md :

Documentation in markdown files can be updated directly in the master branch, unless the documentation is in the source code, and the patch changes line numbers.

[PhilGlass]

@dkhalanskyjb Done. FWIW I read that section and wasn't sure whether it applied to KDoc changes - it mentions markdown files, but this PR touches a Kotlin file with some KDoc/markdown in it. Perhaps worth clarifying.