possible bug when updated for IGRF 14th generation

[MarceloBanik]

Description of the problem
When I updated the mgd77.c, I forgot to correct the value of ll when date >= 2025.
The following git diff should fix it.
git.diff.txt

Full script that generated the error

$ echo "-40 -23 0" | gmt mgd77magref -A+t2030-01-01 -Frdihtxyz/0

Actual outcome

-40     -23     0       -23.6834085446  -45.1126921225  99247.1093732   140633.484713   90888.4135314   -39865.8375639  -99638.2873376

Expected outcome

-40     -23     0       -23.6146017145  -46.9950606818  15934.1328456   23361.7277194   14599.8192634   -6382.93561129  -17084.3124677

These values are compatible with the output from https://www.ngdc.noaa.gov/IAGA/vmod/pyIGRF14.zip

System information

• Operating system: Ubuntu 24.04.1 LTS
• GMT version (gmt --version): 6.6.0_0b2b696_2024.11.26