give cov_regularization a default value to prevent tests from breaking.

hera_pspec/pspecdata.py

@@ -56,7 +56,7 @@ def __init__(self, dsets=[], wgts=[], dsets_std=None, labels=None, beam=None):
         self.spw_range = None
         self.spw_Nfreqs = None
         self.spw_Ndlys = None
-
+        self.cov_regularization = 0.
         # set data weighting to identity by default
         # and taper to none by default
         self.data_weighting = 'identity'