Handle default for `plotTypeData` in validation of visualization tables

[dweindl]

Default is MeanAndSD, but petablint currently fails with:

Unknown plotTypeData: {nan}. Must be one of ['MeanAndSD', 'MeanAndSEM', 'replicate', 'provided']

see e.g. https://github.com/Benchmarking-Initiative/Benchmark-Models-PEtab/actions/runs/5576504114/jobs/10187882534?pr=187