fix: add Docker APT repository before installing docker-ce

The rootless_docker.yml task was trying to apt install docker-ce
without first adding the Docker APT repository, causing package not
found errors on Debian/Ubuntu containers.

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

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

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

@@ -1,4 +1,21 @@
 ---
+- name: Install Docker GPG key (Debian/Ubuntu)
+  ansible.builtin.get_url:
+    url: "https://download.docker.com/linux/{{ ansible_facts['distribution'] | lower }}/gpg"
+    dest: "{{ docker_gpg_key_path }}"
+    mode: "0644"
+  when: ansible_facts['os_family'] == 'Debian'
+
+- name: Add Docker APT repository (Debian/Ubuntu)
+  ansible.builtin.apt_repository:
+    repo: >-
+      deb [arch={{ ansible_facts['architecture'] }} signed-by={{ docker_gpg_key_path }}]
+      https://download.docker.com/linux/{{ ansible_facts['distribution'] | lower }}
+      {{ ansible_facts['distribution_release'] }} stable
+    state: present
+    update_cache: true
+  when: ansible_facts['os_family'] == 'Debian'
+
 - name: Install rootless Docker dependencies (Debian/Ubuntu)
   ansible.builtin.apt:
     name: