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-bridge-mx-puppet-steam/tasks/setup_install.yml

@@ -83,6 +83,8 @@
     repo: "{{ matrix_mx_puppet_steam_container_image_self_build_repo }}"
     dest: "{{ matrix_mx_puppet_steam_docker_src_files_path }}"
     force: "yes"
+  become: true
+  become_user: "{{ matrix_user_username }}"
   register: matrix_mx_puppet_steam_git_pull_results
   when: "matrix_mx_puppet_steam_enabled|bool and matrix_mx_puppet_steam_container_image_self_build"