Describe the bug

Apparently any entries of type std:label from objects.inv are purely ignored/not-recognize, making impossible lo link to documentation.

To Reproduce

Lets analyze a practical example, https://docs.ansible.com/ansible/latest/objects.inv which can be converted to text for debugging via sphobjinv convert plain objects.inv objects.txt.

I will be listing some of the txt output here:

Ansible.get_bin_path py:method 1 api/index.html#$ -
developing_galaxy std:label -1 galaxy/dev_guide.html#developing-galaxy Galaxy Developer Guide

• Using [Ansible.get_bin_path][] works as expected.
• Using [developing_galaxy][] does not work and produces, Could not find cross-reference target '[developing_galaxy]'

It seems that std:label entries are not recognized but py:method ones are.

Expected behavior

Be able to link any entries from objects.inv.

Information (please complete the following information):

mkdocstrings==0.19.1
mkdocstrings-python==0.8.3

Additional context