test/pybind/test_rados.py: fix test_list_objects

Commit 6662e6b accidentally removed a line from this test.

```
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:=================================== FAILURES ===================================
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:_________________________ TestIoctx.test_list_objects __________________________
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:self = <test_rados.TestIoctx object at 0x7fddcc6924c0>
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:    def test_list_objects(self):
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:        self.ioctx.write('b', b'foo')
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:        self.ioctx.write_full('c', b'bar')
2024-05-21T14:06:10.463 INFO:tasks.workunit.client.0.smithi031.stdout:        self.ioctx.append('d', b'jazz')
2024-05-21T14:06:10.464 INFO:tasks.workunit.client.0.smithi031.stdout:        object_names = [obj.key for obj in self.ioctx.list_objects()]
2024-05-21T14:06:10.464 INFO:tasks.workunit.client.0.smithi031.stdout:>       eq(sorted(object_names), ['a', 'b', 'c', 'd'])
```

Signed-off-by: Matan Breizman <[email protected]>

Author: Matan-B

src/test/pybind/test_rados.py

@@ -318,6 +318,7 @@ def test_read_crc(self):
         self.ioctx.read('a')
 
     def test_list_objects(self):
+        self.ioctx.write('a', b'')
         self.ioctx.write('b', b'foo')
         self.ioctx.write_full('c', b'bar')
         self.ioctx.append('d', b'jazz')