models/MontagueDayanSejnowski: Use versioned seaborn style

[jvesely]

Plain names are deprecated in matplotlib and removed in matplotlib==3.8.0. The versioned name with underscore was introduced in matplotlib==3.7.0, 6608eedfc6f33f723f1e13c6025a5b918c7c9f6d ("Re-rename builtin seaborn styles to not include a dot.")