Arguments work! Yay!

.gitlab-ci.yml

@@ -27,5 +27,5 @@ build-git:
   except:
     - pushes
   script:
-    - docker build --pull -t "$CI_REGISTRY_IMAGE:$GRAV_VERSION-git" ./git/
+    - docker build --pull --build-arg "CI_COMMIT_SHORT_SHA=$CI_COMMIT_SHORT_SHA" -t "$CI_REGISTRY_IMAGE:$GRAV_VERSION-git" ./git/
     - docker push "$CI_REGISTRY_IMAGE:$GRAV_VERSION-git"

git/Dockerfile

@@ -1,3 +1,4 @@
+ARG CI_COMMIT_SHORT_SHA
 FROM williammiceli/grav:$CI_COMMIT_SHORT_SHA
 
 # Install Git