GitHub Actions: Changes to artifact download experience

We have changed the artifact download experience in GitHub Actions so it no longer adds an extra root directory to the downloaded archive.

Previously, if you uploaded the following files and folders as an artifact named `foo`, the downloaded archive would contain the following structure:

foo/
 |-- file1.txt
 |-- dir1/
 |    |-- dir1-file1.txt

Now, you will get an archive that only contains the files and folders you uploaded:

file1.txt
dir1/
|-- dir1-file1.txt