Amend doc

Author: EugeneFlesselle

tests/pos/typeclass-encoding3b.scala

@@ -347,10 +347,10 @@ object functors {
   MonadFlatten.flattened(List(List(1, 2, 3), List(4, 5))) // ok, synthesizes (using ListMonad)
   MonadFlatten.flattened(List(List(1, 2, 3), List(4, 5)))(using ListMonad) // was an error
   /*
-  When checking `ListMonad <:< functors.Monad.Impl[T]`
-  we eventually get to the comparison `[X] =>> T[X] <:< [+X] =>> List[X]`
+  Before the changes, when checking `ListMonad <:< functors.Monad.Impl[T]`
+  we eventually got to the comparison `[X] =>> T[X] <:< [+X] =>> List[X]`
   because the `This` type member of `ListMonad` has a covariance annotation.
-  This fails the variance conformance checks despite the fact that T has been instantiated to List,
-  since it has been substituted into the refinement (and cached) before its instantiation.
+  This failed the variance conformance checks despite the fact that T had been instantiated to List,
+  since it had been substituted into the refinement (and cached) before its instantiation.
   */
 }