Warnings in the examples

[stefaniapedrazzi]

I tested the version on the master branch.
I tried to test on Iron but many packages for the robots (TIAGo, TurtleBot) are not available so I switched to Humble.

Everything works fine apart from some warnings:

• many worlds are using EXTERNPROTO declaration pointing to the develop branch even in the webots_ros2/master branch causing compatibility warnings
• TurtleBot3 simulations throw errors about an excessive motor velocity

  WARNING: TurtleBot3Burger "TurtleBot3Burger" > DEF RIGHT_JOINT HingeJoint > RotationalMotor "right wheel motor": The requested velocity quested velocity 17.8473 exceeds 'maxVelocity' = 6.67.
  WARNING: TurtleBot3Burger "TurtleBot3Burger" > DEF LEFT_JOINT HingeJoint > RotationalMotor "left wheel motor": The requested velocity 12.4558 exceeds 'maxVelocity' = 6.67.
  

Just a note: as reported in #496, snap Webots doesn't work with webots_ros2 on Ubuntu 22.04 due to different OpenSSL version that prevents downloading the assets.