[skip-ci] Packit: downstream package name at package level

Packit doesn't honor a global `downstream_package_name` key when the
upstream repo and downstream package name don't match. For this very
repo, upstream repo is `common`, while downstream package is
`containers-common`.

For such cases, `downstream_package_name` should be specified at the
package level.

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>

.packit.yaml

@@ -2,14 +2,15 @@
 # See the documentation for more information:
 # https://packit.dev/docs/configuration/
 
-downstream_package_name: containers-common
 upstream_tag_template: v{version}
 
 packages:
   containers-common-fedora:
+    downstream_package_name: containers-common
     pkg_tool: fedpkg
     specfile_path: rpm/containers-common.spec
   containers-common-centos:
+    downstream_package_name: containers-common
     pkg_tool: centpkg
     specfile_path: rpm/containers-common.spec