Fix git-latest ansible-lint errors

Reference: https://ansible-lint.readthedocs.io/en/latest/default_rules/#git-latest

Our variable naming is not necessarily consistent across roles.
I've tried to follow the naming conventions of each individual role.
All new variables are suffixed with `_version`, but the prefix may be
somewhat different.

roles/matrix-bot-matrix-registration-bot/defaults/main.yml

@@ -5,6 +5,7 @@
 matrix_bot_matrix_registration_bot_enabled: true
 matrix_bot_matrix_registration_bot_container_image_self_build: false
 matrix_bot_matrix_registration_bot_docker_repo: "https://github.com/moan0s/matrix-registration-bot.git"
+matrix_bot_matrix_registration_bot_docker_repo_version: "{{ matrix_bot_matrix_registration_bot_version if matrix_bot_matrix_registration_bot_version != 'latest' else 'main' }}"
 matrix_bot_matrix_registration_bot_docker_src_files_path: "{{ matrix_bot_matrix_registration_bot_base_path }}/docker-src"
 
 matrix_bot_matrix_registration_bot_version: latest

roles/matrix-bot-matrix-registration-bot/tasks/setup_install.yml

@@ -36,6 +36,7 @@
 - name: Ensure matrix-registration-bot repository is present on self-build
   ansible.builtin.git:
     repo: "{{ matrix_bot_matrix_registration_bot_docker_repo }}"
+    version: "{{ matrix_bot_matrix_registration_bot_docker_repo_version }}"
     dest: "{{ matrix_bot_matrix_registration_bot_docker_src_files_path }}"
     force: "yes"
   become: true