Add test for not failing with Python 3.12

It seems Python 3.12 changed the behavior of unittest to fail if no test
as run at all.

Author: bjoernricks

tests/__init__.py

@@ -14,3 +14,10 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+
+
+class DummyTestCase(unittest.TestCase):
+    def test_dummy(self):
+        pass