Enable the stable copr repository for building (#3452)

This will allow us to test with fresh `fmf` bits as soon as they
are released. We will not have to wait until packages reach the
stable fedora repositories.

.packit.yaml

@@ -34,6 +34,8 @@ _:
   # Copr jobs under the packit project
   - &copr-under-packit
     job: copr_build
+    additional_repos:
+      - copr://@teemtee/stable
 
   # Copr jobs under the teemtee project
   - &copr-under-teemtee
@@ -46,6 +48,14 @@ _:
   - &test-base
     job: tests
     trigger: pull_request
+    tf_extra_params:
+      environments:
+        - &copr-teemtee-stable
+          artifacts:
+            - type: repository-file
+              id: https://copr.fedorainfracloud.org/coprs/g/teemtee/stable/repo/fedora-rawhide/group_teemtee-stable-fedora-rawhide.repo
+            - type: repository-file
+              id: https://copr.fedorainfracloud.org/coprs/g/teemtee/stable/repo/epel-9/group_teemtee-stable-epel-9.repo
 
   # Latest fedora & epel targets
   - &latest-targets
@@ -60,6 +70,7 @@ _:
     tf_extra_params:
       environments:
         - &tmt-cloud-resources
+          <<: *copr-teemtee-stable
           settings:
             provisioning:
               tags:
@@ -124,7 +135,7 @@ jobs:
         - tmt:
             context:
               how: provision
-        - *tmt-cloud-resources
+          <<: *tmt-cloud-resources
 
   # Test internal plugins
   - <<: *test-base