CI: clearfog: keep the work dir as an artifact

A regular build (i.e., a change uploaded to br2-external) should also
create a compressed tarball of Buildroot's working directory. This will
be used later on as a starting state for jobs triggered by, say,
cla-sysrepo.

Interestingly, I'm not getting a `staging/` directory when in CI, but
I'm seeing it locally. The docs say it's a backward-compatible thingy,
so let's just skip it.

Also, do not upload the U-Boot SPL when being triggered externally.

Change-Id: I7ac4edf6d1775192e17f0cefc77c25dac979b9e6
diff --git a/.zuul.yaml b/.zuul.yaml
index 0b5bc96..208ce46 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -2,6 +2,7 @@
     name: czechlight-clearfog
     parent: run-ci-build-sh-f31
     timeout: 3600
+    post-timeout: 600
     vars:
       prepare_git_submodules: true
       zuul_work_dir: "{{ zuul.projects['cesnet-gerrit-czechlight/CzechLight/br2-external'].src_dir }}"
@@ -35,5 +36,17 @@
 - project:
     check:
       jobs:
-        - czechlight-clearfog
+        - czechlight-clearfog:
+            provides: CzechLight-br2-build-clearfog
+            vars:
+              artifacts:
+                name: br2-work-dir
+                glob: 'br2-work-dir-*.tar.zst'
+            post-run: ci/post.yaml
+            roles:
+              - zuul: return-built-artifact
         - czechlight-beagleboneblack
+
+    promote:
+      jobs:
+        - promote-artifacts