Lint that module nf-tests use a single config with sourcing the args from params

[mahesh-panchal]

Description of feature

From nf-core/website#2832 (comment)

More importantly do we have an issue to create linting around this?

what exactly should we lint for?

A single nextflow.config file in tests, and that it contains the string ext.args = params., and not ext.args = [{'"]

Also the same if ext.prefix is used. Check the string starts with ext.prefix = params. Although I'm not sure if ext.prefix has a need to be used in a test config.