There is no Mixed element support in fenics. The aim is to support this in the future in dolfinx.
Note that the support for quarilateral/hexahedral elements in dolfin is quite limited, and i strongly advice you to move to dolfinx if you require such elements.
Using the following arguments in gmsh will force all cells to be quadrilateral:
Recombine Surface {:};
Mesh.RecombinationAlgorithm = 2;