Change camera info message to lower case (#1005)

Change camera info message to lower case since message type had been
change in rolling and humble.
[](https://github.com/ros2/common_interfaces/blob/rolling/sensor_msgs/msg/CameraInfo.msg)

camera_calibration/src/camera_calibration/camera_checker.py

@@ -172,9 +172,9 @@ def handle_monocular(self, msg):
             object_points = self.mc.mk_object_points(
                 [self.board], use_board_size=True)[0]
             dist_coeffs = numpy.zeros((4, 1))
-            camera_matrix = numpy.array([[camera.P[0], camera.P[1], camera.P[2]],
-                                         [camera.P[4], camera.P[5], camera.P[6]],
-                                         [camera.P[8], camera.P[9], camera.P[10]]])
+            camera_matrix = numpy.array([[camera.p[0], camera.p[1], camera.p[2]],
+                                         [camera.p[4], camera.p[5], camera.p[6]],
+                                         [camera.p[8], camera.p[9], camera.p[10]]])
             ok, rot, trans = cv2.solvePnP(
                 object_points, image_points, camera_matrix, dist_coeffs)
             # Convert rotation into a 3x3 Rotation Matrix