CI: "Fix" the Coverity job

James Browningrequested to merge
jamesb_fe80/ntpsec:2026-05-Coverity-a into master

Dump the Coverity HTTP response headers to the log, and exit with amber 255 error if the received file isn't gzipped.

This might be too much, and it may be too little. Either way, having more info than "something went wrong" will be useful.

The parts have been tested in isolation, but not this combination.

Merge request reports