RuboCop: Target Rails version 7.0

What does this MR do and why?

We've switched to Rails 7.0 some time ago and are now using 7.0.5.

No changes/new offenses expected.

With this, rules which require Rails 7+ can now be enabled:

• Rails/ToSWithArgument
• Rails/ToFormattedS

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.