Add SetupTools to our functional testing venvs

With the upcoming addition of Python 3.12 testing, we need to make
sure venvs where we'll be invoking or importing setuptools have its
package preinstalled, as the newer versions of venv don't include it
by default any longer.

Change-Id: Ia5d9247afa562d4d84d1acb345ac08dd39713bb6

pbr/tests/test_packaging.py

@@ -186,7 +186,7 @@ class Venv(fixtures.Fixture):
         """
         self._reason = reason
         if modules == ():
-            modules = ['pip', 'wheel', 'build', PBR_ROOT]
+            modules = ['pip', 'wheel', 'build', 'setuptools', PBR_ROOT]
         self.modules = modules
         if pip_cmd is None:
             self.pip_cmd = ['-m', 'pip', '-v', 'install']