ci(release): hardcode external Gitea registry host

GITHUB_SERVER_URL inside act_runner resolves to gitea:3000 (internal
docker hostname) which is not reachable from the build job container.
Use the externally-resolvable hostname instead.

.github/workflows/release-image.yml

@@ -36,12 +36,11 @@ jobs:
 
       - id: registry
         name: Resolve Gitea registry host
-        # GITHUB_SERVER_URL is the Gitea base URL (e.g. https://gitea.hartmut-noerenberg.com).
-        # Strip the scheme to get the container-registry host.
+        # GITHUB_SERVER_URL inside act_runner resolves to the *internal* Gitea
+        # hostname (gitea:3000) which is not reachable from the job container.
+        # Hardcode the externally-resolvable host instead.
         run: |
-          host="${GITHUB_SERVER_URL#https://}"
-          host="${host#http://}"
-          echo "host=${host}" >> "$GITHUB_OUTPUT"
+          echo "host=gitea.hartmut-noerenberg.com" >> "$GITHUB_OUTPUT"
 
       - name: Login to Gitea container registry
         # GITHUB_TOKEN is auto-provisioned by Gitea Actions for the running