Use alpine for deploying nightly tag.

ci/deploy.gitlab-ci.yml

@@ -1,14 +1,13 @@
  # Push a nightly tag if the pipeline succeeded.
 deploy:tag:nightly:
   stage: deploy
-  image: ubuntu:latest
+  image: alpine:edge
+  dependencies: []
   before_script:
-    - export DEBIAN_FRONTEND=noninteractive
-    - apt-get update -y
-    - apt-get install -y --no-install-recommends git
+    - apk add git
   script:
     - git tag -f nightly $CI_COMMIT_SHORT_SHA
-    - git push $EIGEN_CI_GIT_PUSH_URL tag nightly
+    - git push -f $EIGEN_CI_GIT_PUSH_URL tag nightly
   tags:
     - linux
     - eigen-runner