message: Minor fix in ek.set_grad, ek.accum_grad
diff: @@ -2003,7 +2003,7 @@ def grad(a):
  def set_grad(a, value):
  - if _ek.is_diff_array_v(a):
  + if _ek.is_diff_array_v(a) and a.IsFloat:
  if _ek.is_diff_array_v(value):
  value = _ek.detach(value)
  @@ -2015,12 +2015,10 @@ def set_grad(a, value):
  elif _ek.is_enoki_struct_v(a):
  for k in type(a).ENOKI_STRUCT.keys():
  set_grad(getattr(a, k), value)
  - else:
  - raise Exception("Expected a differentiable array type!")
  def accum_grad(a, value):
  - if _ek.is_diff_array_v(a):
  + if _ek.is_diff_array_v(a) and a.IsFloat:
  if _ek.is_diff_array_v(value):
  value = _ek.detach(value)
  @@ -2032,8 +2030,6 @@ def accum_grad(a, value):
  elif _ek.is_enoki_struct_v(a):
  for k in type(a).ENOKI_STRUCT.keys():
  accum_grad(getattr(a, k), value)
  - else:
  - raise Exception("Expected a differentiable array type!")
  def grad_enabled(a):
  