assertion failed: duplicate type F#7718; previous was type F#7369 (using Scala 2 published `cats-effect`)

[scf37]

Compiler version

3.0.0-RC1 and 3.0.0-RC2

Minimized code & Output

https://scastie.scala-lang.org/EzwUElRQS2uavuyN6TU4ow

Another one:
https://scastie.scala-lang.org/Kx6GbNFJRPenigB5LiOdxg

Expectation

Successful compilation

[griggt]

Both examples seem to work fine when depending on the Scala 3 published cats-effect artifact instead of using .withDottyCompat to get the Scala 2 artifact.

---

Aside: is there some reason that Scastie uses Scala 2 libraries and .withDottyCompat in Scala 3 build mode, even when Scala 3 published versions are available? This doesn't always work and can be quite confusing, as seen here and in this recent issue on gitter re: ScalaTest: https://gitter.im/lampepfl/dotty?at=6067745692a3431fd66fa63b

[griggt]

Duplicate of #11173