Fix type of mask

The call here was creating a float64 array, which was turning many
downstream scores into float64s. Later on these values were assigned to
a float32 array in backprop, and numerical underflow caused things to go
to zero.

That's almost certainly not the only reason things go to zero, but it is
incorrect.

spacy/ml/models/coref.py

@@ -373,7 +373,7 @@ def ant_scorer_forward(
             warnings.filterwarnings('ignore', category=RuntimeWarning)
             mask = xp.log(
                 (xp.expand_dims(ant_range, 1) - xp.expand_dims(ant_range, 0)) >= 1
-            ).astype(float)
+            ).astype('f')
 
         scores = pw_prod + pw_sum + mask