fix: add default(0) to gitea_runner_uid in environment blocks

Ansible evaluates environment blocks even when when conditions are
false. The deregister scenario sets skip_runner_registration: true
but the environment block still references gitea_runner_uid, causing
"variable is undefined" errors. Add default(0) filter to prevent
this.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

ansible/roles/gitea-runner/tasks/deregister.yml

@@ -30,8 +30,8 @@
   become: true
   become_user: "{{ gitea_runner_service_user }}"
   environment:
-    XDG_RUNTIME_DIR: "/run/user/{{ gitea_runner_uid }}"
-    DOCKER_HOST: "unix:///run/user/{{ gitea_runner_uid }}/docker.sock"
+    XDG_RUNTIME_DIR: "/run/user/{{ gitea_runner_uid | default(0) }}"
+    DOCKER_HOST: "unix:///run/user/{{ gitea_runner_uid | default(0) }}/docker.sock"
   when:
     - runner_file_stat.stat.exists | default(false) | bool
     - not skip_runner_registration

ansible/roles/gitea-runner/tasks/register.yml

@@ -25,8 +25,8 @@
   become: true
   become_user: "{{ gitea_runner_service_user }}"
   environment:
-    XDG_RUNTIME_DIR: "/run/user/{{ gitea_runner_uid }}"
-    DOCKER_HOST: "unix:///run/user/{{ gitea_runner_uid }}/docker.sock"
+    XDG_RUNTIME_DIR: "/run/user/{{ gitea_runner_uid | default(0) }}"
+    DOCKER_HOST: "unix:///run/user/{{ gitea_runner_uid | default(0) }}/docker.sock"
   when: not runner_registered.stat.exists
   register: register_output
   changed_when: "'already exists' not in register_output.stdout | default('')"