Fix wrong context for docker.io username

Author: EZForever

.github/workflows/build.yml

@@ -80,6 +80,6 @@ jobs:
           image_name: ${{ github.repository }}
           image_tag: server-${{ matrix.ssl }}-${{ matrix.avx }}
           github_token: ${{ secrets.GHCR_ACCESS_TOKEN }}
-          docker_io_user: ${{ env.DOCKER_IO_USER }}
+          docker_io_user: ${{ vars.DOCKER_IO_USER }}
           docker_io_token: ${{ secrets.DOCKER_IO_ACCESS_TOKEN }}