Plugin file can't be downloaded when `plugin.yml` is replaced by `paper-plugin.yml`

[Neocky]

When testing with Veinminer from modrinth this will cause pluGET to say that the plugin was not correctly downloaded because the plugin.yml file was not found. Veinminer has only a paper-plugin.yml file in their root plugin archive. We test it the same way in the plugin_downloader.py. This needs to be fixed across pluGET so it will check if one of the files is present.
I will create an issue for that. You can change it or leave it as this mirrors currently the same behaviour across all platforms.

Originally posted by @Neocky in https://github.com/Neocky/pluGET/pull/87#discussion_r2301672273