Update for Gravity Correction Fix

Tactac, Kevinrequested to merge
defect13759_fixGravityCorrectionSign into main

CIS found that the sign of an equation is wrong, so this MR updates reference values as a result

13759: [lr_reduction] Gravity Reduction Sign

https://github.com/neutrons/LiquidsReflectometer/pull/88

Edited by Tactac, Kevin

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