Pass index.docker.io explicitly

Signed-off-by: Nic Cope <nicc@rk0n.org>

.github/workflows/ci.yml

@@ -90,11 +90,8 @@ jobs:
           build-args:
             GO_VERSION=${{ env.GO_VERSION }}
           load: true
-          tags: function-runtime:${{ github.sha }}
+          tags: function/runtime:${{ github.sha }}
 
-      - name: List Docker Images
-        run: docker image ls
-
       # TODO(negz): Use the crossplane-contrib/xpkg-action for this? It doesn't
       # currently do anything other than download the CLI and run a command.
       - name: Setup the Crossplane CLI
@@ -103,8 +100,10 @@ jobs:
           XP_CHANNEL: master
           XP_VERSION: current
 
+      # TODO(negz): We must pass index.docker.io explicitly until 
+      # https://github.com/crossplane/crossplane/pull/4867 is fixed.
       - name: Build Package
-        run: ./crossplane xpkg build --package-root=package/ --embed-runtime-image=function-runtime:${{ github.sha }}
+        run: ./crossplane xpkg build --package-root=package/ --embed-runtime-image=index.docker.io/function/runtime:${{ github.sha }}
 
       - name: Login to Upbound
         uses: docker/login-action@v3