Basic test case: copr build only

This test case is triggered automatically by our validation script.

```yaml
- job: copr_build
  trigger: pull_request
  metadata:
    targets:
    - fedora-all
```

.packit.yaml

@@ -14,8 +14,7 @@ jobs:
   trigger: pull_request
   metadata:
     targets:
-    - fedora-stable-x86_64
-    - fedora-rawhide-x86_64
+    - fedora-all
 
 - job: copr_build
   trigger: release
@@ -30,13 +29,6 @@ jobs:
     targets:
       - fedora-stable
 
-- job: tests
-  trigger: pull_request
-  metadata:
-    targets:
-    - fedora-stable-x86_64
-    - fedora-rawhide-x86_64
-
 - job: propose_downstream
   trigger: release
   packit_instances: ["stg"]