ci: Test dist'ing as well

.gitlab-ci.yml

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8a113c8..6eb20d4 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -33,6 +33,7 @@
     - ninja -C build/ install
     - .ci/check-abi ${LAST_ABI_BREAK} $(git rev-parse HEAD)
     - ninja -C build/ test
+    - ninja -C build/ dist
 
 reference:
   stage: document