Specify CI test stage platform dependencies

If dependencies between a platform's build and test jobs are not
specified, then artifacts from all platforms' build jobs are passed to
each test job. This is not what we want!

https://docs.gitlab.com/ee/ci/yaml/#dependencies

.gitlab-ci.yml

@@ -8,7 +8,7 @@ cache:
     - ccache/
 
 # Building inkscape
-inkscape:
+inkscape:linux:
   stage: build
   before_script:
     # CCache Config
@@ -56,6 +56,7 @@ inkscape:mac:
     paths:
       - build/
   allow_failure: true
+
 # This job is a static analysis build by clang.
 # It takes MORE THAN 3 HOURS, and depending on worker sometimes 4 hours.
 # Make sure the timeout of the build is big enough
@@ -73,8 +74,10 @@ clang:
     paths:
       - scan/
 
-test:
+test:linux:
   stage: test
+  dependencies:
+    - inkscape:linux
   script:
     - cd build
     - make test