test: update correct number of columns test

Now prior columns are named 'prior_bias', 'prior_sq_err'

tests/test_obs_sequence.py

@@ -47,8 +47,8 @@ def test_read1d(self, obs_seq_file_path):
         obj = obsq.obs_sequence(obs_seq_file_path)
         assert obj.loc_mod == 'loc1d'
         assert len(obj.df) == 40  # 40 obs in the file
-        assert obj.df.columns.str.contains('posterior').sum() == 22 + 2  # members + sq_err + bias
-        assert obj.df.columns.str.contains('prior').sum() == 22
+        assert obj.df.columns.str.contains('posterior').sum() == 24  # 20 members + mean + spread + sq_err + bias
+        assert obj.df.columns.str.contains('prior').sum() == 24