Stopping the mixing -> clear separation Forgejo/Github

This action is even less useful in Github than in Forgejo/Gitea so let's stop
wasting time and clearly label with a suffix 'v4.x.y-github' for Github.

.github/workflows/generate-release-zipfile.yml

@@ -1,9 +1,7 @@
 on:
   push:
     branches:
-      # Difference between Github and Forgejo : with the former, an empty
-      # 'branches' key means "nothing" while the later understands it as "all".
-      #- '*'
+      - 'v4-github'
 
 jobs:
   GenerateReleaseZipfile: