relax tolerance in tests/gauss_point_buoyancy/gauss_point_buoyancy.xml
relax tolerance in tests/gauss_point_buoyancy/gauss_point_buoyancy.xml

jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jrper/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity