ci(server-image): publish to GHCR only by manual dispatch from master

Publishing a GitHub Release, stable or pre-release, now only validates the
server image. A desktop release and a server image release are separate
owner decisions, so a stable desktop release cannot publish an image that
has not been accepted yet.

.github/workflows/server-image.yml

@@ -114,8 +114,7 @@ jobs:
   publish:
     if: >-
       github.repository == 'ajisaacs/OpenNest' &&
-      ((github.event_name == 'release' && github.event.release.prerelease == false) ||
-       (github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/master'))
+      github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     timeout-minutes: 40
     permissions: