CI: Install file-dev in alpine release targets

.gitlab-ci.yml

@@ -217,7 +217,7 @@ amd64-musl:
   cache: *release-cache
   variables: *release-variables
   before_script: &before-release-musl
-  - apk add git gcc g++ musl-dev make cmake
+  - apk add git gcc g++ musl-dev make cmake file-dev
   - echo "import Mix.Config" > config/prod.secret.exs
   - mix local.hex --force
   - mix local.rebar --force