Address CRAN issue

── Failure ('test-Model-validity.R:237:3'): v_model_logistic_normal_fixed_mix returns message for weights and comp of diff len ── Expected `v_model_logistic_normal_fixed_mix(object)` to equal "components must have same length as weights". Differences: actual vs expected "components must have same length as weights" - "weights must sum to 1"