[cherry-pick] fix tal assigner cr (#7731)

ppdet/modeling/assigners/task_aligned_assigner_cr.py

@@ -178,4 +178,4 @@ class TaskAlignedAssigner_CR(nn.Layer):
         alignment_metrics = alignment_metrics.max(-2).unsqueeze(-1)
         assigned_scores = assigned_scores * alignment_metrics
 
-        return assigned_labels, assigned_bboxes, assigned_scores
+        return assigned_labels, assigned_bboxes, assigned_scores, mask_positive