Fixes publishing to github container registry (INTO-CPS-Association#987)

The github container registry expects organization scope to be
lowercase. This PR converts org scope to lowercase even if it is
uppercase.

.github/workflows/docker-ghcr.yml

@@ -1,6 +1,6 @@
 # Reusable workflow for building and pushing a Docker Image to GHCR.
 # 
-# Username is taken from the user who scheduled the workflow
+# Username is the repository owner converted to lowercase
 # Password is taken from the auto-generated GitHub token
 
 name: Build and Push Docker Image (GHCR)
@@ -21,7 +21,6 @@ on:
 
 env:
   registry: ghcr.io
-  ghcr-scope: ${{ github.repository_owner }}
   password: ${{ secrets.GITHUB_TOKEN }}
 
 jobs:
@@ -36,6 +35,14 @@ jobs:
       - name: Checkout Repository
         uses: actions/checkout@v4
 
+      # Sets a new environment variable that can be accessed in later
+      # steps via ${{ env.ghcr-scope }}
+      - name: Get repository owner in lower-case
+        run: |
+          echo "ghcr-scope=${REPOSITORY_OWNER,,}" >> $GITHUB_ENV
+        env:
+          REPOSITORY_OWNER: ${{ github.repository_owner }}
+
       - name: Log in to the Container registry
         uses: docker/login-action@v3
         with: