Update -n parameter in %setup macro

[StykMartin]

GitHub archives are created with the repository name as a prefix.

For instance, requesting an archive from:

https://github.com/beaker-project/beaker/archive/beaker-28.3.tar.gz

results in a file named beaker-beaker-28.3.tar.gz, as indicated by the content-disposition header:

</snip>
< content-disposition: attachment; filename=beaker-beaker-28.3.tar.gz
</snip>

Although the Spectool and RPM toolchain store the file based on the requested path, resulting in beaker-28.3.tar.gz, the internal structure of the tarball reflects the original GitHub archive naming. This discrepancy can cause issues during the RPM build process.

This commit adjusts the %setup -n parameter in the spec file to align with the GitHub archive's internal structure, ensuring correct extraction and building.

The change has been manually tested in COPR and with rpmbuild/spectool.
We can't catch this problem in CI right now because of the way Packit works. Packit replaces both sources and the %setup macro.