Extract pull zone id in CI script into a variable

Author: pimterry

.github/workflows/ci.yml

@@ -128,7 +128,8 @@ jobs:
         run: |
           # Clear CDN cache to re-request content:
           curl -f --request POST \
-            --url https://api.bunny.net/pullzone/1110200/purgeCache \
+            --url https://api.bunny.net/pullzone/$PULL_ZONE_ID/purgeCache \
             --header "AccessKey: $BUNNY_SITE_API_KEY"
         env:
+          PULL_ZONE_ID: 1110200
           BUNNY_SITE_API_KEY: ${{ secrets.BUNNY_SITE_API_KEY }}