purge CDN cache on deploy (#2526)

* purge CDN cache on deploy

issues a purge all to the Fastly service that fronts peps.python.org to make new changes appear fast..... lier.

* yaml?

.github/workflows/render.yml

@@ -39,3 +39,11 @@ jobs:
           branch: gh-pages # The branch to deploy to.
           folder: build # Synchronise with build.py -> build_directory
           single-commit: true # Delete existing files
+
+      - name: ♻️  Purge CDN cache
+        if: github.ref == 'refs/heads/main'
+        run: |
+          curl -H "Accept: application/json" -H "Fastly-Key: $FASTLY_TOKEN" -X POST "https://api.fastly.com/service/$FASTLY_SERVICE_ID/purge_all"
+        env:
+          FASTLY_TOKEN: ${{ secrets.FASTLY_TOKEN }}
+          FASTLY_SERVICE_ID: ${{ secrets.FASTLY_SERVICE_ID }}