ci: Add artifacts for style check job

It is not easy to find out  why the style check job failed. Let's expose
the style check job diff over artifacts to make it easier.

.gitlab-ci.yml

@@ -79,7 +79,14 @@ triage:dry-run:
 style check:
     image: registry.gitlab.gnome.org/gnome/nautilus:latest
     stage: test
+    artifacts:
+        name: 'Style check artifacts'
+        expose_as: 'Get style check diff here'
+        when: on_failure
+        paths:
+            - 'uncrustify.diff'
+        expire_in: 14 days
     script:
         - gcc data/lineup-parameters.c `pkg-config --cflags --libs gio-2.0 gio-unix-2.0` -o data/lineup-parameters
         - LANG=C.utf8 data/run-uncrustify.sh
-        - git diff --exit-code
+        - git diff --exit-code | tee uncrustify.diff