Compiler bug: `constValue` was not evaluated by the compiler

## Compiler version
3.0.0-RC1, 3.0.0-RC2

## Minimized code & Output

https://scastie.scala-lang.org/ehjkJuUmQQamcw6HC27N4g

## Expectation

No "compiler bug" message. Also, I was unable to find out what is 'constant type' and why my type is not constant
