GitHub Actions: Test mixed-version clusters against RabbitMQ 4.0.5

... instead of 4.0.3.

[Why]
We need the following bugfixes:
* one in the Khepri reset code backported in #12739 and published in
  RabbitMQ 4.0.4.
* one in the quorum queue code backported in #12850 and published in
  RabbitMQ 4.0.5.

Author: dumbbell

.github/workflows/test-make-target.yaml

@@ -57,7 +57,8 @@ jobs:
       uses: dsaltares/fetch-gh-release-asset@master
       if: inputs.mixed_clusters
       with:
-        version: 'tags/v4.0.3'
+        repo: 'rabbitmq/server-packages'
+        version: 'tags/alphas.1732832828710'
         regex: true
         file: "rabbitmq-server-generic-unix-\\d.+\\.tar\\.xz"
         target: ./