packit.yml: fix archive name

This was a mistake introduced in osbuild#2041.

Author: croissanne

packit.yaml

@@ -39,8 +39,8 @@ jobs:
       # same as the global one, but specifying actions: does not inherit
       post-upstream-clone: make spec
       create-archive:
-        - sh -exc "curl -L -O https://github.com/osbuild/cockpit-composer/releases/download/${PACKIT_PROJECT_VERSION}/${PACKIT_PROJECT_NAME_VERSION}.tar.xz"
-        - sh -exc "ls ${PACKIT_PROJECT_NAME_VERSION}.tar.xz"
+        - sh -exc "curl -L -O https://github.com/osbuild/cockpit-composer/releases/download/${PACKIT_PROJECT_VERSION}/${PACKIT_PROJECT_NAME_VERSION}.tar.gz"
+        - sh -exc "ls ${PACKIT_PROJECT_NAME_VERSION}.tar.gz"
 
   - job: propose_downstream
     trigger: release