[netcdfgroup] API bump in 4.7.4

[Marco Atzeri <marco.atzeri@xxxxxxxxx>]

Hi Dev,
I am a bit surprised to find a API bump between two minor release

  libnetcdf_la_LDFLAGS = -version-info 17:1:2

  libnetcdf_la_LDFLAGS = -version-info 18:0:0

specially as there is no notice on the release news

  https://github.com/Unidata/netcdf-c/releases

Has the binary compatibility been broken or it is a mistake ?

Regards
Marco