Remove numpy array warning filter

[veenstrajelmer]

Reported in #1243 and implemented #1244. The filter is now added in netCDF4: reported in Unidata/netcdf4-python#1354 (comment) and implemented in Unidata/netcdf4-python#1471.

Todo:

• await netCDF4 release (>1.7.4, after 23 feb 2026)
• remove warning filter
• maybe require updating the minimal required netcdf4 version
• see if tests still pass