docs(ci): move deployment to different stage

.github/workflows/docs.yml

@@ -21,10 +21,7 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  build-and-deploy:
-    permissions:
-      pages: write
-      id-token: write
+  build:
     # Don't run on forks
     if: github.repository == 'prefix-dev/pixi'
     runs-on: ubuntu-latest
@@ -63,6 +60,11 @@ jobs:
         with:
           path: "site"
 
+  deploy:
+    runs-on: ubuntu-latest
+    needs: build
+    if: github.repository == 'prefix-dev/pixi' && github.ref == 'refs/heads/main'
+    steps:
       - name: Deploy to GitHub Pages
         id: deployment
         uses: actions/deploy-pages@v2