chore: update rubocop requirement from ~> 1.67.0 to ~> 1.68.0

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.67.0...v1.68.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

instrumentation/base/opentelemetry-instrumentation-base.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'minitest', '~> 5.0'
   spec.add_development_dependency 'opentelemetry-test-helpers', '~> 0.3'
   spec.add_development_dependency 'rake', '~> 13.0'
-  spec.add_development_dependency 'rubocop', '~> 1.67.0'
+  spec.add_development_dependency 'rubocop', '~> 1.68.0'
   spec.add_development_dependency 'rubocop-performance', '~> 1.22.0'
   spec.add_development_dependency 'simplecov', '~> 0.22.0'
   spec.add_development_dependency 'yard', '~> 0.9'