/usr/share/gretl/scripts/misc/longley.inp is in gretl-common 1.9.14-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # Classic test for ill-conditioned data
open longley.gdt
ols 1 0 2 3 4 5 6 7 --vcv
vif
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