copr-hypervisors: define undefined variable

It is sometimes not needed, so default it to 0.

roles/copr/backend/files/provision/provision_builder_tasks.yml

@@ -1,4 +1,12 @@
 ---
+- name: default copr_builder_fedora_version
+  set_fact:
+    copr_builder_fedora_version: 0
+  when:
+    - copr_builder_fedora_version is not defined
+  tags:
+    - always
+
 # TODO: Drop this entirely once we are on F35+
 - name: remove the hackish package breaking s390x subscriptions
   shell:

roles/copr/backend/templates/provision/vars.yml

@@ -1,7 +1,7 @@
 ---
 devel: {% if devel is defined and devel %}true{% else %}false{% endif %}
 
-copr_builder_fedora_version: {{ copr_builder_fedora_version | default(0) }}
+copr_builder_fedora_version: {{ copr_builder_fedora_version }}
 
 {% if copr_red_hat_subscription_password is defined %}
 copr_red_hat_subscription_password: "{{ copr_red_hat_subscription_password }}"