epath behaves weird using fsspec on gcs

Via GCloud Console I clicked "CREATE FOLDER" to create `empty_folder`.
Then I did:

```python
$ touch /tmp/test.txt
$ gsutil cp /tmp/test.txt gs://henning-test/folder/test.txt

$ python
Python 3.10.12 (main, Nov 20 2023, 15:14:05) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from etils import epath
>>> epath.gpath._is_tf_installed()
False
>>> e = epath.Path('gs://henning-test/empty_folder')
>>> f'{e.exists()=} {e.is_dir()=}'
'e.exists()=True e.is_dir()=False'
>>> list(e.iterdir())
[PosixGPath('gs://henning-test/empty_folder')]

>>> f = epath.Path('gs://henning-test/folder')
>>> f'{f.exists()=} {f.is_dir()=}'
'f.exists()=True f.is_dir()=False'

>>> t = epath.Path('gs://henning-test/folder/test.txt')
>>> f'{t.exists()=} {t.is_dir()=}'
't.exists()=True t.is_dir()=False'
>>> list(t.iterdir())
[PosixGPath('gs://henning-test/folder/test.txt/test.txt')]
```