Fix EdgeNoPartialVarAssignCheck for projections in multi-assignments
Adding the following to the `EdgeNoPartialVarAssignCheck.cif` test does not make that test fail, even though there is a new projected variable assignment on an edge, because the projection is inside a multi-assignment.
```
automaton partialInMulti:
disc int x;
disc tuple(int a, b) y;
location:
initial;
edge do (x, y[0]) := (1, 2);
end
```
Note that:
* The check is not used anywhere directly.
* The check is part of `EdgeOnlySimpleAssignmentsCheck`, which is used by CIF to Supremica and CIF to UPPAAL. Neither supports multi-assignments.
* As such, the bug is currently (on 2024-03-17) not visible to end users.
* The multi-level synthesis tool will include `EdgeOnlySimpleAssignmentsCheck` as well, in !696. So that one is not affected either.
issue