Merge pull request #7904 from dotty-staging/fix-#7879

Fix #7879: Turn test case into neg test

Author: odersky

tests/neg/i7879.scala

@@ -0,0 +1,4 @@
+object Test {
+  val head1 +: _ = List(1).view
+  val _: Int = head1  // error
+}