Extract needs items that includesPlant UML

[BCristianRazvan]

Describe the bug:

• Every time when .. needextract:: is used on needs elements that includes Plant UML file will cause a sphinx-needs error on needuml.py file when is indexed

To reproduce:

.. req:: My_req
   :id: REQ_1

   Description

   .. include:: diagram.puml

.. needextract::
   :type: req
   :filter: "REQ_" in id

Expected behaviour:
needextract should also retrieve and display the Plant UML details from the needs we want to extract.

Desktop (please complete the following information):

OS: Linux in Devcontainer
Architecture x64
Sphinx-need 5.0.0