fix(CI): Ensure eluna is installed for acore-docker (#17530)

.github/workflows/docker_build.yml

@@ -94,6 +94,18 @@ jobs:
 
       - uses: actions/checkout@v4
 
+      # The containers created in this workflow are used by
+      # acore-docker, which has a dependency on mod-eluna.
+      #
+      # If you're wanting containers without mod-eluna, the best solution is to
+      # build them locally (such as with `docker compose build`)
+      - name: Download Eluna
+        if: github.repository == "azerothcore/azerothcore-wotlk" && github.ref_name == 'master'
+        uses: actions/checkout@v4
+        with:
+          repository: azerothcore/mod-eluna
+          path: modules/mod-eluna
+
       - name: Login to Docker Hub
         if: github.repository == 'azerothcore/azerothcore-wotlk' && github.ref_name == 'master'
         uses: docker/login-action@v1