Use QPointF to avoid TypeError in Python3.10

Close #1203

labelme/widgets/canvas.py

@@ -699,10 +699,10 @@ class Canvas(QtWidgets.QWidget):
         if (x, y) == (x1, y1):
             # Handle cases where previous point is on one of the edges.
             if x3 == x4:
-                return QtCore.QPoint(x3, min(max(0, y2), max(y3, y4)))
+                return QtCore.QPointF(x3, min(max(0, y2), max(y3, y4)))
             else:  # y3 == y4
-                return QtCore.QPoint(min(max(0, x2), max(x3, x4)), y3)
-        return QtCore.QPoint(x, y)
+                return QtCore.QPointF(min(max(0, x2), max(x3, x4)), y3)
+        return QtCore.QPointF(x, y)
 
     def intersectingEdges(self, point1, point2, points):
         """Find intersecting edges.