Merge #7151

7151: Bump rubocop to 0.68.0 r=hsbt a=deivid-rodriguez

### What was the end-user problem that led to this PR?

The problem was that our rubocop version is getting outdated. Also, I added [a PR to rubocop](rubocop/rubocop#6935) so that we can remove the exclusions in our configuration, and it has now been released.

### What is your fix for the problem, implemented in this PR?

My fix is to update rubocop to the latest version, update the configuration, and fix new offenses.

Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>