Gitlab CI: Specify image architecture for arm64 images

.gitlab-ci.yml

@@ -253,7 +253,7 @@ arm64:
   only: *release-only
   tags:
     - arm
-  image: elixir:1.10.3
+  image: arm64v8/elixir:1.10.3
   cache: *release-cache
   variables: *release-variables
   before_script: *before-release
@@ -265,8 +265,7 @@ arm64-musl:
   only: *release-only
   tags:
     - arm
-  # TODO: Replace with upstream image when 1.9.0 comes out
-  image: elixir:1.10.3-alpine
+  image: arm64v8/elixir:1.10.3-alpine
   cache: *release-cache
   variables: *release-variables
   before_script: *before-release-musl