Fix WreathProductElementList to not modify its list argument

[FriedrichRober]

Replace StructuralCopy with ShallowCopy in WreathProductElementListNC.

Otherwise an immutable list representation from the input gets replaced with the wreath product element even outside of the scope of WreathProductElementList.

Setup:

gap> K := FreeGroup("x", "y");;
gap> AssignGeneratorVariables(K);;
gap> H := SymmetricGroup(3);;
gap> W := WreathProduct(K, H);
<group with 4 generators>
gap> l := [x*y, x, y, (1,2,3)];
[ x*y, x, y, (1,2,3) ]
gap> MakeImmutable(l);;
gap> w := WreathProductElementList(W, l);
WreathProductElement(x*y,x,y,(1,2,3))

Current behaviour: list l gets overwritten by output w.

gap> l;
WreathProductElement(x*y,x,y,(1,2,3))

Expected behaviur: list l should be unchanged

gap> l;
[ x*y, x, y, (1,2,3) ]

Text for release notes

Fix a bug in WreathProductElementList for generic wreath products, which replaced an immutable list from the input with the constructed wreath product element.

[james-d-mitchell]

Perhaps add a test?

[fingolfin]

Thanks, fix makes sense. But it would indeed be nice you could add your example as a test case.