Fix Git import for nested export folders

[cnra]

Hi, first of all, thanks for this great addon. It helps a lot!

I ran into a small problem:

I had an Anki deck named cryllic for learning the Cyrillic alphabet and tried using it with CrowdAnki. I exported it, but I chose to export it into a custom folder named anki-cryllic, since that seemed more suitable for GitHub usage with a clearer name.

The exporter created an additional nested folder named cryllic inside the anki-cryllic directory. I then pushed this structure to GitHub in this repository:

https://github.com/cnra/anki-cryllic

Then I tried to import it from GitHub. However, the import failed because deck.json was not found. The file was not at the root of the repository checkout, but inside the nested folder.

I inspected the code and saw that nested directories were already considered, but only under the assumption that the nested folder name is the same as the root folder name. In this example, it was not.

This fix makes the import logic more general: it now finds deck.json wherever it exists inside the nested export directory.