astro/gpscorrelate: update to v2.3

gpscorrelate has a new maintainer, Dan Fandrich,
and the former maintainer, Daniel Foote, recognizes the change.
https://github.com/freefoote/gpscorrelate?tab=readme-ov-file#status

Update the port to the new location,
https://dfandrich.github.io/gpscorrelate/
update to v2.3, switch to Github downloads, hook up self-test suite,
make DOCS and (new) NLS options work right.

Reported by: Dan Fandrich
see also: https://github.com/dfandrich/gpscorrelate/issues/36

ChangeLog: https://raw.githubusercontent.com/dfandrich/gpscorrelate/refs/tags/2.3/RELEASES