One that doesn't trip up ansible-lint, causing `load-failure` 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.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939