Bump rubocop to 1.68.0

Hi there 😄 I'm using right now ruby-lsp and vscode to work on GitLab's code. There seems to be a problem with the rubocop version 1.67, that might have been fixed in version 1.68. https://github.com/Shopify/ruby-lsp/issues/2840#issuecomment-2471661847 Since I'm not able to run several cops with ruby-lsp, we need to bump the version to 1.68.