[gnome-tetravex] Try to fix CI.

[Arnaud B. <arnaudb src gnome org>]

commit 6d2b45e6013d85c036e57e7bf76b0119bcf3aafd
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Fri Jun 12 17:26:20 2020 +0200

    Try to fix CI.

 build-aux/org.gnome.Tetravex.json | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/build-aux/org.gnome.Tetravex.json b/build-aux/org.gnome.Tetravex.json
index 9fac1b5..d2c0bff 100644
--- a/build-aux/org.gnome.Tetravex.json
+++ b/build-aux/org.gnome.Tetravex.json
@@ -19,6 +19,7 @@
     ],
     "modules": [{
         "name": "gnome-tetravex",
+        "buildsystem": "meson",
         "sources": [{
             "type": "git",
             "url": "https://gitlab.gnome.org/GNOME/gnome-tetravex.git";