Clarify which registry is used

- PRs/branches: ghcr
- merged: DockerHub

Author: Michael Vasseur

.github/workflows/build-contributor-container-PR.yml

@@ -19,7 +19,7 @@ jobs:
         uses: docker/setup-qemu-action@v3
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
-      - name: Login to Docker Hub
+      - name: Login to GitHub container registry
         uses: docker/login-action@v3
         with:
           registry: ghcr.io

.github/workflows/build-contributor-container-release.yml

@@ -22,7 +22,6 @@ jobs:
       - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:
-          registry: ghcr.io
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 

.github/workflows/build-domjudge-container-PR.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Login to Docker Hub
+      - name: Login to GitHub container registry
         uses: docker/login-action@v3
         with:
           registry: ghcr.io