ci: fix lowercase in publication

Author: uwu-loli

.github/workflows/docker-publish.yml

@@ -9,6 +9,7 @@ on:
 
 env:
   REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
 
 jobs:
   build-and-push:
@@ -21,9 +22,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set lowercase repository name
-        run: echo "IMAGE_NAME=${GITHUB_REPOSITORY,,}" >> $GITHUB_ENV
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3