Fix pybullet sim package.xml leading to warning during build

Author: Flova

bitbots_simulation/bitbots_pybullet_sim/package.xml

@@ -27,6 +27,7 @@
   <depend>python3-numpy</depend>
 
   <export>
+    <build_type>ament_cmake</build_type>
     <bitbots_documentation>
       <status>unknown</status>
       <language>python</language>