fzn-gecode, maximum_arg, abort on co-occurrences

On Ubuntu 22.04.2 LTS.
```
$ cat /tmp/latest.mzn
include "globals.mzn";
var 1..2 union 4..6: A;
var 1..7: B;
var 1..3 union 5..7: C;
var 1..1 union 7..7: D;
var 1..4 union 6..7: E;
constraint
maximum_arg([C,B,D,A,E],A);
$ minizinc /tmp/latest.mzn
Error: Gecode: Int::argmax: Argument array contains same variable multiply
```