x11/showmethekey: Update to 1.18.3
ChangeLog:
Updated to fix undefined XKB_MOD_NAME_MOD5 in old XKBcommon
Updated to adapt virtual modifier changes in XKBcommon v1.8
MFH: 2025Q2
(cherry picked from commit d5f9d44dc1ccb89b7046d0454c90ff95e7d47258)