CI: Fix hopeless-docker prevention

[why]
I am sure I tested it and it worked. Well, it does not, it throws an
error message
  Unrecognized named-value: 'secrets'

[how]
Secrets can not be used in the `if`, see
https://github.com/actions/runner/issues/520

But they can be used in `env`, ... so do it there.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

.github/workflows/docker-release.yml

@@ -17,7 +17,7 @@ jobs:
   publish-image:
     name: Publish image
     runs-on: ubuntu-latest
-    if: ${{ secrets.DOCKER_USER }}
+    if: ${{ github.repository_owner == 'ryanoasis' }}
     steps:
       - uses: actions/checkout@v3
       - name: Build image