fix double type promotion (#1901)

python/tests/test_double.py

@@ -173,6 +173,16 @@ class TestDouble(mlx_tests.MLXTestCase):
             mx.allclose(y, y_double.astype(mx.float32, mx.cpu), equal_nan=True)
         )
 
+    def test_type_promotion(self):
+        import mlx.core as mx
+
+        a = mx.array([4, 8], mx.float64)
+        b = mx.array([4, 8], mx.int32)
+
+        with mx.stream(mx.cpu):
+            c = a + b
+            self.assertEqual(c.dtype, mx.float64)
+
 
 if __name__ == "__main__":
     unittest.main()