Update tests to 3.8

Author: odersky

tests/neg/localReaches.check

@@ -2,9 +2,9 @@
 24 |  var x: () ->{xs*} Unit = ys.head // error
    |                           ^^^^^^^
    |                           Local reach capability ops* leaks into capture scope of method localReach3.
-   |                           To allow this, the parameter ops should be declared with a @use annotation.
+   |                           You could try to abstract the capabilities referred to by ops* in a capset variable.
 -- Error: tests/neg/localReaches.scala:27:11 ---------------------------------------------------------------------------
 27 |    x = ys.head  // error
    |        ^^^^^^^
    |        Local reach capability ops* leaks into capture scope of method localReach3.
-   |        To allow this, the parameter ops should be declared with a @use annotation.
+   |        You could try to abstract the capabilities referred to by ops* in a capset variable.

tests/pos/cc-use-alternatives.scala

@@ -1,3 +1,4 @@
+//> using options -source 3.7
 import language.experimental.captureChecking
 // no separation checking
 import caps.{cap, use}