Merged requested to merge gthain/cmake:retry-file-download-on-timeout into master
Since !5034 (merged) ExternalProject has a list of curl errors which trigger a retry today: 6, 7, 8 and 15.
Add curl error 28. It is a "timeout error", and should also trigger a retry attempt at a download of an external project. The complete list of curl errors is https://curl.se/libcurl/c/libcurl-errors.html