Merge pull request #9128 from dotty-staging/fix-#8956

fix #8956: add regression test

Author: odersky

tests/pos-special/fatal-warnings/i8956.scala

@@ -0,0 +1,16 @@
+type Numeric = Double | Int
+
+val v1 = 100
+val v2 = 100.0
+def check1(i: Double | Int | String): Unit = {
+  i match {
+    case a:(Double | Int) => println(s"numeric = $a")
+    case _ => println("categorical")
+  }
+}
+def check2(i: Double | Int | String): Unit = {
+  i match {
+    case a:Numeric => println(s"numeric = $a")
+    case _ => println("categorical")
+  }
+}