Bump gitlab-styles v7.0.0

What does this MR do and why?

This MR does 2 things:

• Bump gitlab-styles to v7.0.0, see diff
• Add existing offenses to rubocop_todo.yml for new cop introduced with v7.0.0

$ REVEAL_RUBOCOP_TODO=0 bundle exec rubocop -p --only RSpec/VerifiedDoubles spec ee/spec | grep -o ".*spec.*.rb" | awk '{print $1}' > verified_doubles.yml
$ REVEAL_RUBOCOP_TODO=0 bundle exec rubocop -p --only RSpec/InstanceVariable spec ee/spec | grep -o ".*spec.*.rb" | awk '{print $1}' > instance_variables.yml
$ REVEAL_RUBOCOP_TODO=0 bundle exec rubocop -p --only GraphQL/ArgumentUniqueness app/graphql | grep -o ".*spec.*.rb" | awk '{print $1}' > argument_uniqueness.yml
$ REVEAL_RUBOCOP_TODO=0 bundle exec rubocop -p --only GraphQL/UnusedArgument app/graphql | grep -o ".*spec.*.rb" | awk '{print $1}' > unused_argument.yml

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.