Update Docker workflow to use Gitea registry and credentials for image publishing

Signed-off-by: Stephen Simpson <ssimpson89@users.noreply.github.com>

.github/workflows/docker-image-linux.yml

@@ -3,8 +3,8 @@ on:
   - push
   - workflow_dispatch
 env:
-  REGISTRY: ghcr.io
-  GITHUBUSER: ${{ github.repository_owner }}
+  REGISTRY: gitea.sjs.io
+  GITHUBUSER: ${{ gitea.repository_owner }}
   IMAGE_NAME: speedtest-cli
 jobs:
   build-and-push-image:
@@ -26,14 +26,14 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITEA_TOKEN }}
 
       - name: Extract metadata for Docker
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.REGISTRY }}/${{ env.GITHUBUSER }}/${{ env.IMAGE_NAME }}
+          images: ${{ env.REGISTRY }}/${{ env.GITEAUSER }}/${{ env.IMAGE_NAME }}
           tags: |
             type=raw,value=latest
             type=sha,format=short