fix CI for users with no installer-test cachix

Closes #5173

.github/workflows/test.yml

@@ -4,6 +4,7 @@ on:
   push:
 jobs:
   tests:
+    needs: [check_cachix]
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
@@ -16,6 +17,7 @@ jobs:
     - uses: cachix/install-nix-action@v13
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v10
+      if: needs.check_cachix.outputs.secret == 'true'
       with:
         name: '${{ env.CACHIX_NAME }}'
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'