[BUG] Setting pml sizes in 2D

[djps]

Describe the bug
It is not possible to set pml_x_size and pml_y_size using a two-item list pml_size. Instead only the first value is taken.

This is not the case for 3D simulations.

Expected behavior
I'd expect that the pml lengths in x and y are assigned from both entries in the list pml_size