Fix Pinocchio unit tests (error not caught)

Stretch description failed but exception was not caught by pytest. With
unittest it is.

Author: stephane-caron

tests/loaders/test_idyntree.py

@@ -18,9 +18,9 @@
 import unittest
 
 from robot_descriptions._descriptions import DESCRIPTIONS
-
 from robot_descriptions.loaders.pinocchio import load_robot_description
 
+
 class TestPinocchio(unittest.TestCase):
 
     """
@@ -44,6 +44,7 @@ def test(self):
 
         return test
 
+
 # Add a test function for each URDF description
 for name, description in DESCRIPTIONS.items():
     if description.has_urdf:

tests/loaders/test_pinocchio.py

@@ -46,48 +46,42 @@ commands =
 [testenv:loader-idyntree]
 deps =
     idyntree >= 8.0.0
-    pytest
 commands =
-    pytest --import-mode=importlib tests/loaders/test_idyntree.py
+    python -m unittest tests/loaders/test_idyntree.py
 
 [testenv:loader-mujoco]
 deps =
     mujoco >=2.2.1
-    pytest
 commands =
-    mujoco: pytest --import-mode=importlib tests/loaders/test_mujoco.py
+    python -m unittest tests/loaders/test_mujoco.py
 
 [testenv:loader-pinocchio]
 deps =
     pin >=2.6.14
-    pytest
 commands =
-    pytest --import-mode=importlib tests/loaders/test_pinocchio.py
+    python -m unittest tests/loaders/test_pinocchio.py
 
 [testenv:loader-pybullet]
 deps =
     numpy >=1.23.4
     pybullet >=3.2.5
-    pytest
 commands =
-    pytest --import-mode=importlib tests/loaders/test_pybullet.py
+    python -m unittest tests/loaders/test_pybullet.py
 
 [testenv:loader-robomeshcat]
 deps =
     pycollada >=0.6
-    pytest
     robomeshcat >= 1.0.4
 commands =
-    pytest --import-mode=importlib tests/loaders/test_robomeshcat.py
+    python -m unittest tests/loaders/test_robomeshcat.py
 
 [testenv:loader-yourdfpy]
 deps =
     numpy >=1.23.4
-    pytest
     trimesh ~=3.16.0
     yourdfpy >=0.0.53
 commands =
-    pytest --import-mode=importlib tests/loaders/test_yourdfpy.py
+    python -m unittest tests/loaders/test_yourdfpy.py
 
 [pylint]
 generated-members=mujoco.MjModel, pin.JointModelFreeFlyer, pin.JointModelPX, pin.JointModelPY, pin.JointModelPZ, pin.JointModelPlanar, pin.JointModelRX, pin.JointModelRY, pin.JointModelRZ, pin.JointModelSpherical, pin.JointModelSphericalZYX, pin.JointModelTranslation, pin.Model, pybullet.loadURDF, pybullet.setAdditionalSearchPath