See if this works.

.gitea/workflows/build.yml

@@ -31,6 +31,12 @@ jobs:
       - name: Set up Docker Buildx
         uses: https://github.com/docker/setup-buildx-action@2b51285047da1547ffb1b2203d8be4c0af6b1f20 # v3
 
+      - name: "Add Cargo registry"
+        run: |
+          echo '[registries.gitea]' \
+            'index = "sparse+https://git.toast-server.net/api/packages/toast/cargo/"' \
+            'token = "Bearer ${{ secrets.CARGO_TOKEN }}"' > ~/.cargo/config.toml
+
       - name: Build and push image
         uses: https://github.com/docker/build-push-action@2cdde995de11925a030ce8070c3d77a52ffcf1c0 # v5.3.0
         with: