Avoid generating skolems just to return true

Co-authored-by: Guillaume Martres <[email protected]>

Author: dwijnand

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -523,7 +523,9 @@ class SpaceEngine(using Context) extends SpaceLogic {
   /** Is `tp1` a subtype of `tp2`?  */
   def isSubType(tp1: Type, tp2: Type): Boolean = trace(i"$tp1 <:< $tp1", debug, show = true) {
     if tp1 == constantNullType && !ctx.explicitNulls then tp2 == constantNullType
-    else adaptType(tp1, tp2) <:< tp2
+    else
+      isPrimToBox(tp1, tp2) || isPrimToBox(tp2, tp1) ||
+      convertConstantType(tp1, tp2) <:< tp2
   }
 
   def isSameUnapply(tp1: TermRef, tp2: TermRef): Boolean =