[x64] jnp.packbits: avoid implicit promotion of boolean inputs

Why? Under the new strict promotion flag, booleans promotion to integer will error.
This change makes it so that jnp.packbits still works with strict promotion enabled.

jax/_src/numpy/lax_numpy.py

@@ -3314,7 +3314,7 @@ def packbits(a, axis: Optional[int] = None, bitorder='big'):
     raise TypeError('Expected an input array of integer or boolean data type')
   if bitorder not in ['little', 'big']:
     raise ValueError("'order' must be either 'little' or 'big'")
-  a = greater(a, 0).astype('uint8')
+  a = lax.gt(a, _lax_const(a, 0)).astype('uint8')
   bits = arange(8, dtype='uint8')
   if bitorder == 'big':
     bits = bits[::-1]