Edge case for names of variables

A variable name of the form "x_1m" e.g. will fail here:
```
julia> short_name = short_names[1]
"iwc_1m"

julia> var = get(simdir; short_name)
ERROR: Variable iwc_1m not found. Available: Set(Any["si", "et", "trans", "swc", "ct", "msf", "lwp", "swu", "swe", "iwc", "gpp", "lwu"])
```
even though the file (`iwc_1m_1M_average.nc`) is present. This may because the code assumes "_1m" refers to the time interval of a minute.

Reproduce the failure with short_name set to "iwc_1m" and call get(simdir; short_name) against the shown NetCDF file. Inspect the variable-name parsing around that entry point; done means the existing iwc_1m_1M_average.nc file is recognized without misinterpreting "_1m" as a time interval.

Written by the indexing model from the issue text.