If I try to load a NetCDF file created using ncgen from:
```
netcdf hyb_ht_test {
dimensions:
lev = 2 ;
lat = 1 ;
lon = 1 ;
time = UNLIMITED ; // (1 currently)
variables:
double b…
If I load the first NetCDF file dumped below (hyb_ht_test) using Iris 1.5.1 then a HybridHeightFactory is automatically generated to produce a derived altitude coordinate (which is the behaviour I wou…