Bump minimum python version to skip backport.

Some APIs used were not introduced until 3.10 so use the backport unless
we have it.

Author: nuclearsandwich

setup.py

@@ -21,8 +21,8 @@
         'catkin_pkg >= 0.4.3',
         'setuptools',
         'empy < 4',
-        'importlib-metadata; python_version < "3.8"',
-        'importlib-resources; python_version < "3.8"',
+        'importlib-metadata; python_version < "3.10"',
+        'importlib-resources; python_version < "3.10"',
         'packaging',
         'python-dateutil',
         'PyYAML',