CP-311905: fix make test failure

Signed-off-by: Chunjie Zhu <chunjie.zhu@cloud.com>

Author: chunjiez

opam/tgroup.opam

@@ -1,5 +1,6 @@
 # This file is generated by dune, edit dune-project instead
 opam-version: "2.0"
+synopsis: "Thread group management library"
 maintainer: ["Xapi project maintainers"]
 authors: ["xen-api@lists.xen.org"]
 license: "LGPL-2.1-only WITH OCaml-LGPL-linking-exception"