Attempt to make Renovate work for docker.io/devture/exim-relay

It seems like with the default versioning detection strategy (`docker`),
the version is detected up to the hyphen:

> Renovate tries to follow the most common conventions that are used to tag Docker images.
> In particular, Renovate treats the text after the first hyphen as a type of platform/compatibility indicator.

Perhaps with `semver` would be more appropriate for this image.

More details in: https://docs.renovatebot.com/modules/versioning/

roles/custom/matrix-mailer/defaults/main.yml

@@ -10,7 +10,7 @@ matrix_mailer_container_image_self_build_repository_url: "https://github.com/dev
 matrix_mailer_container_image_self_build_src_files_path: "{{ matrix_mailer_base_path }}/docker-src"
 matrix_mailer_container_image_self_build_version: "{{ matrix_mailer_docker_image.split(':')[1] }}"
 
-# renovate: datasource=docker depName=devture/exim-relay
+# renovate: datasource=docker depName=devture/exim-relay versioning=semver
 matrix_mailer_version: 4.96.2-r0-0
 matrix_mailer_docker_image: "{{ matrix_mailer_docker_image_name_prefix }}devture/exim-relay:{{ matrix_mailer_version }}"
 matrix_mailer_docker_image_name_prefix: "{{ 'localhost/' if matrix_mailer_container_image_self_build else matrix_container_global_registry_prefix }}"