fix: Only add external version warning nodes on documents

[elenakrittik]

For some reaosn, Sphinx emits doctree-resolved not only for documents (in our case it was emitted with docutils.nodes.bullet_list as doctree), which causes external version warning to appear in unexpected places (sidebar in our case). This PR adds simple isinstance() check which ensures that doctree is sphinx.addnodes.document, eliminating the above issue.

Resolves #113

[humitos]

Hrm... Interesting. I think I've experienced this with out own blog recently where the banner was added to multiple places:

@ItsAleph Is this the issue that you were experimenting as well?

[onerandomusername]

@ItsAleph Is this the issue that you were experimenting as well?

@humitos We had something similar, but not quite the same as yours. (I'm working on the same project as @ItsAleph)

[elenakrittik]

Yeah, i had similar issue, this warning was injected into main page, and also in sidebar.
Above

[humitos]

Looks good to me! Thanks.

I'm requesting review from another developer as well, just to have some extra eyes as backup :)

[stsewd]

From sphinx's typehints, it's said that these are documents

https://github.com/sphinx-doc/sphinx/blob/2f1d92773cc6e2857c6d4a0fd30caecbbfd5d4b3/sphinx/environment/__init__.py#L567-L582

so, this might be a sphinx bug... I'll see if I can replicate with other versions of sphinx.

[stsewd]

Ok, so from sphinx-doc/sphinx#3796 and some extensions https://github.com/search?q=org%3Asphinx-contrib+resolve_references&type=code.

Sphinx always does use resolve_references with a document node, but that function can be used by extensions, and they may not pass a document node.