Unit fails to build against njs 0.8.2 and libxml2 2.12, or njs 0.8.3

[remicollet]

According to https://github.com/nginx/unit/blob/master/auto/njs#L28

unit requires njs >= 0.8.0

njs 0.8.2 is not compatible with recent libxml2 2.12 njs 0.8.3 recently released is compatible, but introduces API change and is not usable by nginx/unit

Please update nginx/unit to use njs 0.8.3 (or at least fix the version check)

P.S. libxml 2.12 is default version in Fedora 40 (and probably some other distro)