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/tasks/synapse/setup_install.yml

@@ -25,6 +25,8 @@
         dest: "{{ matrix_synapse_docker_src_files_path }}"
         version: "{{ matrix_synapse_docker_image.split(':')[1] }}"
         force: "yes"
+      become: true
+      become_user: "{{ matrix_user_username }}"
       register: matrix_synapse_git_pull_results
 
     - name: Check if Synapse Docker image exists