Consider that Resource.parent can be None when removing resources from the codebase

scancode version: 4b57a7fe86
commoncode version: 32.2.1
python version: 3.13
os: linux

The problematic code:

https://github.com/aboutcode-org/commoncode/blob/aba7c1bdce1477b6b44c4afabd747bd81d9654cf/src/commoncode/resource.py#L908-L918

parent can be None:

https://github.com/aboutcode-org/commoncode/blob/aba7c1bdce1477b6b44c4afabd747bd81d9654cf/src/commoncode/resource.py#L791-L792

None has no `children_names` , it fails. This happens in example if the plugin_ignore of scancode trys to remove some resources from the codebase at: scancode/plugin_ignore.py(121)process_codebase()

How to reproduce:
~~~
❯ scancode --processes 10 -l -p -c -i --ignore "*/test/*" --license-score 20 --strip-root --json-pp test.json repos/git/github/systemd/systemd-stable
Setup plugins...
Collect file inventory...
ERROR: failed to run pre-scan plugin: ignore:
Traceback (most recent call last):
File "/home/jloehel/projects/github.com/aboutcode-org/scancode-toolkit/src/scancode/cli.py", line 1119, in run_codebase_plugins
plugin.process_codebase(codebase, **kwargs)
~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
File "/home/jloehel/projects/github.com/aboutcode-org/scancode-toolkit/src/scancode/plugin_ignore.py", line 121, in process_codebase
remove_resource(resource)
~~~~~~~~~~~~~~~^^^^^^^^^^
File "/home/jloehel/projects/github.com/aboutcode-org/scancode-toolkit/.venv/lib64/python3.13/site-packages/commoncode/resource.py", line 911, in remove_resource
parent.children_names.remove(resource.name)
^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'children_names'
...
~~~

Resource is:
~~~
ScannedResource(path='systemd-stable/test/fuzz/fuzz-unit-file/dev-mapper-fedora_krowka/x2dswap.swap', is_file=True, is_filtered=False, detected_license_expression=None, detected_license_expression_spdx=None, license_detections=[], license_clues=[], percentage_of_license_text=0, copyrights=[], holders=[], authors=[])
~~~