Update rubocop-rspec requirement from ~> 3.7.0 to ~> 3.8.0 (#670)

Updates the requirements on [rubocop-rspec](https://github.com/rubocop/rubocop-rspec) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-rspec/releases)
- [Changelog](https://github.com/rubocop/rubocop-rspec/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rspec@v3.7.0...v3.8.0)

---
updated-dependencies:
- dependency-name: rubocop-rspec
  dependency-version: 3.8.0
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile

@@ -5,4 +5,4 @@ source "https://rubygems.org"
 gemspec
 
 gem "rubocop", "~> 1.81.1", require: false
-gem "rubocop-rspec", "~> 3.7.0", require: false
+gem "rubocop-rspec", "~> 3.8.0", require: false