test(colcon): configure our pkgs to use pytest

to ensure that the CI `colcon test` run works, because with a change to
python 3.12 the `unittest` standard library used by default with colcon
now exits with an error code of 5 for an empty test suite.

See: colcon/colcon-core#678
See: python/cpython#102051

Author: texhnolyze

dynamic_stack_decider/package.xml

@@ -24,6 +24,7 @@
   <depend>rclpy</depend>
   <depend>std_msgs</depend>
   <depend>python3-yaml</depend>
+  <test_depend>python3-pytest</test_depend>
   <test_depend>python3-coverage</test_depend>
 
   <export>

dynamic_stack_decider_visualization/package.xml

@@ -25,6 +25,7 @@
 
   <depend>python3-pydot</depend>
 
+  <test_depend>python3-pytest</test_depend>
 
   <export>
     <architecture_independent/>

dynamic_stack_decider_visualization/setup.py

@@ -12,6 +12,7 @@
         ("share/" + package_name, ["plugin.xml"]),
     ],
     install_requires=["setuptools"],
+    tests_require=["pytest"],
     zip_safe=True,
     entry_points={
         "console_scripts": [