download: handle case of s3 Forbidden

on case of old artifacts which aren't configured to be publicly available
on s3 (Forbidden), we should fallback to download via the
http proxy (downloads.scylladb.com)

ccmlib/utils/download.py

@@ -148,6 +148,10 @@ def download_version_from_s3(url: str, target_path: str, verbose=False):
             logging.warning(f"url: '{url}' wasn't found on S3")
             logging.warning(f"download might be very slow")
             return None
+        elif 'Forbidden' in str(ex):
+            logging.warning(f"url: '{url}' Forbidden (403) on S3")
+            logging.warning(f"download might be very slow")
+            return None
         else:
             raise