More than one variable attribute desired

[ceblanton]

I'm working with a diag yaml that looks like

- file_name: atmos_month_cmip
  time_units: days
  unlimdim: time
  freq: 1 months
  varlist:
  - module: tracers_plev19
    var_name: co2_vmr
    output_name: co2
    reduction: average
    kind: r4
    attributes:
    - pressure_mask: .false.
    - cmip7_name: atmos.co2.tavg-p19-hxy-air.mon.glb

The intent is to have 2 variable attributes, but the schema only allows 1. Let's increase it to 5.