Try pinning cython as less than 3

Author: lmcinnes

hdbscan/_hdbscan_tree.pyx

@@ -106,12 +106,12 @@ cpdef np.ndarray condense_tree(np.ndarray[np.double_t, ndim=2] hierarchy,
             lambda_value = INFTY
 
         if left >= num_points:
-            left_count = <np.intp_t> int(hierarchy[left - num_points][3])
+            left_count = <np.intp_t> hierarchy[left - num_points][3]
         else:
             left_count = 1
 
         if right >= num_points:
-            right_count = <np.intp_t> int(hierarchy[right - num_points][3])
+            right_count = <np.intp_t> hierarchy[right - num_points][3]
         else:
             right_count = 1
 

requirements.txt

@@ -1,4 +1,4 @@
-cython>=0.27
+cython>=0.27,<3
 numpy>=1.20
 scipy>= 1.0
 scikit-learn>=0.20