Use GitHub runners as public repo (#1455)

Based on our [runner selection
documentation](https://hazelcast.atlassian.net/wiki/spaces/EN/pages/5358485538/GitHub+Runner+Selection+Guide),
we should be using the GitHub runners for actions executed in public
repos as they are free vs using paid-for `ubicloud` minutes.

.github/workflows/build-site.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   deploy:
-    runs-on: ubicloud-standard-2
+    runs-on: ubuntu-latest
     steps:
       - name: Dispatch docs deployment
         #   https://docs.netlify.com/configure-builds/build-hooks/