CI: Install libmagic-dev in debian release targets

.gitlab-ci.yml

@@ -198,7 +198,7 @@ amd64:
   variables: &release-variables
     MIX_ENV: prod
   before_script: &before-release
-  - apt-get update && apt-get install -y cmake
+  - apt-get update && apt-get install -y cmake libmagic-dev
   - echo "import Mix.Config" > config/prod.secret.exs
   - mix local.hex --force
   - mix local.rebar --force