Incorrect Keuhn et al. mean_residual_Seattle_basin coeffs

NGA-Sub Keuhn et al. 2020 has incorrect coefficient values for mean_residual_Seattle_basinat 2 and 3 seconds, compared to Keuhn's github repository (https://github.com/nikuehn/KBCG20), see file https://github.com/nikuehn/KBCG20/blob/5d30338436b897822b411553c6ae0bf31fac5ce5/COEFFS_SEP21/coefficients_KBCG20.csv

Also see #86 (closed), #159

changed milestone to %nshm-conus Development

added Bug label

mentioned in merge request !287 (merged)

mentioned in commit 66a535cf

closed with merge request !287 (merged)

changed milestone to %Finalize draft NSHM 2023

changed milestone to %nshm-conus Development