gitlab-ci: add test:debian-stable.

This is going to install the deb artifact created before.

Change-Id: I59a52c8d7fe5dd46bb3ed8684ab3dd477f3baea4
Reviewed-on: https://code.wireshark.org/review/37366
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Dario Lombardo <lomato@gmail.com>

.gitlab-ci.yml

@@ -122,3 +122,14 @@ build:debian-stable:
     paths:
       - debian-packages/*.deb
     expire_in: 3 days
+test:debian-stable:
+  image: debian:stable
+  stage: test
+  script:
+    - apt-get update
+    - DEBIAN_FRONTEND=noninteractive apt-get install ./debian-packages/*.deb -y
+    - tshark --version
+  variables:
+    GIT_STRATEGY: none
+  dependencies:
+    - build:debian-stable