Fix Nonguix substitutes

.github/workflows/build.yaml

@@ -22,13 +22,21 @@ jobs:
       - name: Install Guix
         uses: PromyLOPh/guix-install-action@v1.5
 
+      - name: Set up Nonguix Substitutes
+        run: |
+          # This is necessary to authorize the substitute server
+          wget https://substitutes.nonguix.org/signing-key.pub
+          mv signing-key.pub nonguix-signing-key.pub
+          sudo guix archive --authorize < nonguix-signing-key.pub
+
       - name: Build ISO
         run: |
+          SUBSTITUTE_URLS="--substitute-urls='https://ci.guix.gnu.org https://bordeaux.guix.gnu.org https://substitutes.nonguix.org'"
           # Write out the channels file so it can be included
           guix time-machine -C './guix/base-channels.scm' -- describe -f channels > './guix/channels.scm'
 
           # Build the image
-          image=$(guix time-machine -C './guix/channels.scm' --substitute-urls='https://ci.guix.gnu.org https://bordeaux.guix.gnu.org https://substitutes.nonguix.org' -- system image -t iso9660 './guix/installer.scm')
+          image=$(guix time-machine -C './guix/channels.scm' $SUBSTITUTE_URLS -- system image -t iso9660 $SUBSTITUTE_URLS './guix/installer.scm')
 
           # Copy the image to the local folder with a better name
           export RELEASE_TAG=$(date +"%Y%m%d%H%M")