testdata: add new customization to test data

Author: achilleas-k

testdata/all-fields.in.yaml

@@ -35,6 +35,8 @@ dnf:
       usage:
         install: false
         configure: false
+  config:
+    set_releasever: true
 containers:
   - source: "quay.io/fedora/fedora:latest"
     name: "fedora"

testdata/valid-dnf.in.yaml

@@ -21,3 +21,5 @@ dnf:
       usage:
         install: true
         configure: true
+  config:
+    set_releasever: true