Add a test case there the pattern has a bound

Looking at the log of constr, gadts, and gadtsConstr there seems to be
no change in behaviour compared to before the implementation change in
PatternTypeConstrainer.

Author: dwijnand

tests/pos/i14832.scala

@@ -0,0 +1,7 @@
+class Box[V](val value: V)
+
+class Test:
+  def value: Box["text"] = Box("text")
+
+  def test: String = value match
+    case b: Box[_ <: String] => b.value