Test mirrors using Apple tool

[rgaudin]

Following kiwix/kiwix-apple#1430, we want to make sure whatever requirements apple imposes for our macOS/iOS reader downloads, those are fulfilled by mirrors.

ATM, this means testing using nscurl. ⚠️ it always returns 0 so output needs to be checked instead.

This needs to run on macOS, most likely on different jobs using all the avail macOS images.