[gnome-system-monitor] Add missing -y to ubuntu build test

[Robert Roth <robertroth src gnome org>]

commit 4c6ead600ae211e755cf8abd784db61d6f13f3aa
Author: ToMe25 <tome25 gmx de>
Date:   Mon Sep 13 01:26:52 2021 +0000

    Add missing -y to ubuntu build test

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a36ff7a4..94e8a90f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -80,7 +80,7 @@ build-ubuntu:
     - cd ../.. # build and install libhandy because the version in the ubuntu package repository is too 
outdated.
     - git clone https://gitlab.gnome.org/gnome/libhandy.git/
     - cd libhandy
-    - apt-get build-dep .
+    - apt-get build-dep -y .
     - meson _build
     - ninja -C _build
     - ninja -C _build install