ci: guix: use mirror

.github/workflows/guix.yml

@@ -98,7 +98,7 @@ jobs:
           source /etc/profile.d/zzz-guix.sh
           /usr/local/bin/guix --version
       - name: build
-        run: ADDITIONAL_GUIX_TIMEMACHINE_FLAGS="--disable-authentication" SUBSTITUTE_URLS='https://bordeaux.guix.gnu.org' HOSTS="${{ matrix.toolchain.target }}" ./contrib/guix/guix-build
+        run: ADDITIONAL_GUIX_TIMEMACHINE_FLAGS="--disable-authentication" SUBSTITUTE_URLS='https://bordeaux.guix.gnu.org' GUIX_REPO='https://github.com/monero-project/guix.git' HOSTS="${{ matrix.toolchain.target }}" ./contrib/guix/guix-build
       - uses: actions/upload-artifact@v7
         with:
           name: ${{ matrix.toolchain.target }}

contrib/guix/libexec/prelude.bash

@@ -57,7 +57,7 @@ fi
 # - Check how the update affects our build graph and which packages have been updated.
 time-machine() {
     # shellcheck disable=SC2086
-    guix time-machine --url=https://codeberg.org/guix/guix.git \
+    guix time-machine --url=${GUIX_REPO:-https://codeberg.org/guix/guix.git} \
                       --commit=4a507aa8c0a579d150267d81ab4013189a7ec505 \
                       --cores="$JOBS" \
                       --keep-failed \