specify `cftime` version in environment

When trying to run the GDP container, @kbartels_limno.com and I suddenly got a ValueError: numpy.dtype size changed, may indicate binary incompatibility. Expected 96 from C header, got 88 from PyObject. We initially thought this may be related to the numpy 2.0.0 release on Sunday (https://pypi.org/project/numpy/), but Kieran confirmed that the container was using numpy 1.26.4.

Digging a little more into the error, it apperas it was caused by the lastest release of the latest release of cftime (1.6.4) references changes for numpy 2.0 compatibility. I had to go a release below that (1.6.3) to get the container to run. I got it to work by adding - cftime==1.6.3 to pygeoapi.environment.yml. @ptomasula_limno.com, FYI - this will likely need to be addressed before we merge #95.