memref.alloca_scope and its teminator memref.alloca_scope.return does not register reverse mode AD

The minimal reproducible example is
```
func.func @scope_val(%x: f64) -> f64 {
%r = memref.alloca_scope -> (f64) {
%sq = arith.mulf %x, %x : f64
memref.alloca_scope.return %sq : f64
}
return %r : f64
}

func.func @dscope_val(%x: f64, %dr: f64) -> f64 {
%res = enzyme.autodiff @scope_val(%x, %dr)
{
activity=[#enzyme],
ret_activity=[#enzyme]
} : (f64, f64) -> f64
return %res : f64
}
```