fix typeMemberTouched and add a testcase

Author: Linyxus

compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala

@@ -144,7 +144,7 @@ trait PatternTypeConstrainer { self: TypeComparer =>
               ctx.gadt.bounds(scrut.symbol) match {
                 case tb: TypeBounds =>
                   val hi = tb.hi
-                  constrainPatternType(pat, hi)
+                  constrainPatternType(pat, hi, typeMembersTouched = true)
                 case null => true
               }
             case _ => true

tests/pos/pdgadt-path.scala

@@ -0,0 +1,8 @@
+trait Expr
+case class IntLit(b: Int) extends Expr
+
+def foo[M <: Expr](e: M) = e match {
+  case e1: IntLit =>
+    val t0: e1.type = e
+    val t1: e.type = e1
+}