infra: switch to using generic tag name and manually selecting image

.gitea/workflows/gentoo-utils.yml

@@ -30,7 +30,8 @@ jobs:
         if: steps.image-changes.outputs.changes_detected == 'true'
         uses: docker/setup-buildx-action@v3
 
-      - name: Log in to Github Container Registry
+      -
+        name: Log in to Github Container Registry
         if: steps.image-changes.outputs.changes_detected == 'true'
         uses: docker/login-action@v3
         with:
@@ -38,7 +39,8 @@ jobs:
           username: ${{ vars.CI_BOT_USERNAME }}
           password: ${{ secrets.CI_BOT_TOKEN }}
 
-      - name: Build and push
+      -
+        name: Build and push
         if: steps.image-changes.outputs.changes_detected == 'true'
         uses: docker/build-push-action@v6
         with: