Reenable Gc.compact in Gc tests

Author: jmid

src/gc/stm_tests_spec.ml

@@ -218,7 +218,7 @@ let alloc_cmds, gc_cmds =
           1, return (Major_slice 0); (* cornercase: "If n = 0, the GC will try to do enough work to ensure that the next automatic slice has no work to do" *)
           1, return Major;
           1, return Full_major;
-          (* 1, return Compact; *) (* Temporarily omit Gc.compact to silence the remaining issues: #470 and #480 *)
+          1, return Compact;
         ]) @ alloc_cmds in
     if Sys.(ocaml_release.major,ocaml_release.minor) > (5,3)
     then (1, Gen.return Counters)::gc_cmds  (* known problem with Counters on <= 5.2: https://github.com/ocaml/ocaml/pull/13370 *)