Update rubocop requirement from ~> 1.79.2 to ~> 1.81.6

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@v1.79.2...v1.81.6)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-version: 1.81.6
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile

@@ -18,7 +18,7 @@ group :test do
   gem "climate_control", "~> 1.2.0"
   gem "oj", "~> 3.14" if ENV["WITH_OJ_GEM"] == "true"
   gem "rspec", "~> 3.13.0"
-  gem "rubocop", "~> 1.79.2"
+  gem "rubocop", "~> 1.81.6"
   gem "rubocop-performance", "~> 1.26.0"
   gem "simplecov", "~> 0.22.0"
   gem "simplecov-console", "~> 0.9.1"