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-slack/tasks/setup_install.yml

@@ -80,6 +80,8 @@
     dest: "{{ matrix_mx_puppet_slack_docker_src_files_path }}"
     force: "yes"
     version: "{{ matrix_mx_puppet_slack_container_image_self_build_version }}"
+  become: true
+  become_user: "{{ matrix_user_username }}"
   register: matrix_mx_puppet_slack_git_pull_results
   when: "matrix_mx_puppet_slack_enabled|bool and matrix_mx_puppet_slack_container_image_self_build"