Start downloads right away

There is no need to wait until after validation and linting is done
before beginning the download caching, and it definitely does not need
its own portion of the cycle. Move it to the beginning of the generate
phase, so it gets started up right away.

.gitlab-ci.yml

@@ -1,7 +1,6 @@
 stages:
   - generate
   - lint
-  - cache
   - trigger
 
 variables:
@@ -61,7 +60,7 @@ shellcheck:
 # others were disappearing (e.g. daily builds for Rawhide) before we
 # could get to them
 downloads:
-  stage: cache
+  stage: generate
   retry: 2
   tags:
     - nix