expire the dev history gif in 3 months

Now that we don't refresh master that often, the default expire rule leaves us
without the history animation most of the time. This should add a bit of the
bumper space.

.gitlab-ci.yml

@@ -221,6 +221,7 @@ documentation-assets:gource:
     - docker run -v "$PWD":/visualization $CI_REGISTRY/r3/docker/gource
   artifacts:
     paths: ['output.gif']
+    expire_in: 3 mos
   <<: *global_trigger_build_doc
 
 #