PLCgen: I/O table CSV file 4-cell line confusingly requires only 4 cell-lines
Copied from https://gitlab.eclipse.org/eclipse/escet/escet/-/issues/897#note_2845644
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This feature doesn't work in v5.x. I have tested it with `io.cif` from `plcgen-test-models-v27` and version `nightly-20241023-115319`. In this test I have used the following io table:
```
%I1.0,,in_bool,mijn-Bool
%ID2,,in_int
%ID6,,in_real
%Q1.0,,a.out_bool
%Q1.1,,a.out_alg_bool
%QD2,,a.out_int
%QD6,,a.out_real
```
... and I have received the following error:
Addresses #679
issue