Logic in check_conventions_version qc plugins is misleading

Instead of passing when _any_ of `["CF-1.7", "CF-1.11", "CMIP-6.2"]` are present, they should be split up into CF conventions and CMIP conventions.

E.g. only passing when one of `["CF-1.7", "CF-1.11",]` _and_ `CMIP-6.2` is present.

Or better still would be to move the check for `CMIP` conventions into the compliance checker project plugins `cmip6`, `cmip7`, `cordex`. As checking for `CMIP` isn't part of the `CF` standards.

Also relevant is https://github.com/MetOffice/CDDS/issues/793

Start at the check_conventions_version QC plugins and trace how the CF and CMIP convention lists are evaluated. Review the related CDDS issue #793 and the compliance checker plugins for cmip6, cmip7, and cordex. Done means CF and CMIP checks are no longer conflated, with the intended convention combinations covered by tests.

Written by the indexing model from the issue text.