fix path of artifact upload

uses the img.xz extension since that is registered with the raspberry pi imager

Author: ddaymn

.github/workflows/build-docker.yml

@@ -41,7 +41,7 @@ jobs:
       uses: actions/upload-artifact@v2
       with:
         name: built-image
-        path: ./deploy/image_*PhotonVision.zip
+        path: ./deploy/image_*PhotonVision.img.xz
         if-no-files-found: error
 
     - name: Upload debug artifacts