Tukey window does not require beta parameter

As reported by a competitor in the G2Net CW Kaggle competition, the following set of lines does not throw an error:

$ lalpulsar_Makefakedata_v5 --fmin 10 --Band 1 --IFOs H1 --startTime 100000000 --duration=1800 --outSFTdir=. # Produces H-1_H1_1800SFT_mfdv5-100000000-1800.sft
$ lalpulsar_Makefakedata_v5 --noiseSFTs=H-1_H1_1800SFT_mfdv5-100000000-1800.sft --SFTWindowType=tukey

Specifiying SFTWindowType=tukey is incomplete, for a beta parameter is required to identify a tukey window.

cc @david-keitel @karl-wette