Fix incorrect assignment in Mobject.put_start_and_end_on

PR #3718 changed the behavior of `Mobject.put_start_and_end_on` when
`start == end`, however the assigment to `self.points` was
incorrect. The existing code assigned the Point3D directly to
`self.points`, that then becomes an array with shape `(3,)`, while
instead it should really have shape `(1, 3)`.

This commit fixes the incorrect code and associated test.

manim/mobject/mobject.py

@@ -1771,7 +1771,7 @@ def put_start_and_end_on(self, start: Point3D, end: Point3D) -> Self:
         curr_start, curr_end = self.get_start_and_end()
         curr_vect = curr_end - curr_start
         if np.all(curr_vect == 0):
-            self.points = start
+            self.points = np.array([start])
             return self
         target_vect = np.array(end) - np.array(start)
         axis = (

tests/module/mobject/graphing/test_number_line.py

@@ -126,7 +126,8 @@ def test_point_to_number():
 
 
 def test_start_and_end_at_same_point():
-    line = DashedLine(np.zeros(3), np.zeros(3))
-    line.put_start_and_end_on(np.zeros(3), np.array([0, 0, 0]))
+    point = [1.0, 2.0, 3.0]
+    line = Line(point, point)
+    line.put_start_and_end_on(point, point)
 
-    np.testing.assert_array_equal(np.round(np.zeros(3), 4), np.round(line.points, 4))
+    np.testing.assert_array_equal(np.round([point], 4), np.round(line.points, 4))