Ensure git cloning when self-building is done with the matrix user, not root

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1749

roles/matrix-synapse-admin/tasks/setup.yml

@@ -22,6 +22,8 @@
     dest: "{{ matrix_synapse_admin_docker_src_files_path }}"
     version: "{{ matrix_synapse_admin_docker_image.split(':')[1] }}"
     force: "yes"
+  become: true
+  become_user: "{{ matrix_user_username }}"
   register: matrix_synapse_admin_git_pull_results
   when: "matrix_synapse_admin_enabled|bool and matrix_synapse_admin_container_image_self_build|bool"