GitHub /archive/refs/tags tarball 503/504: fetch the same bytes from codeload.github.com

Some build scripts pin dependency tarballs by sha256 and download them from https://github.com/OWNER/REPO/archive/refs/tags/TAG.tar.gz. When that endpoint returns 503/504, which can last tens of minutes while other GitHub pages still work, fetch https://codeload.github.com/OWNER/REPO/tar.gz/refs/tags/TAG instead. The /archive URL redirects there, and the bytes are the same, so the pinned sha256 still matches (checked for fmt 12.2.0, tomlplusplus v3.4.0 and a boost-regex fork tag). If the build host has the same outage, download on another machine and point the script at a local tarball folder, if it has an override (many do: look for a *_TARBALLS or *_SOURCE env var). Verify the checksums before building.