Update rubocop-minitest requirement from 0.38.2 to 0.39.1 (#218)

Updates the requirements on [rubocop-minitest](https://github.com/rubocop/rubocop-minitest) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-minitest/releases)
- [Changelog](https://github.com/rubocop/rubocop-minitest/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-minitest@v0.38.2...v0.39.1)

---
updated-dependencies:
- dependency-name: rubocop-minitest
  dependency-version: 0.39.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Gemfile

@@ -8,7 +8,7 @@ gem "minitest", "~> 6.0"
 gem "minitest-rg", "~> 5.3"
 gem "rake", "~> 13.0"
 gem "rubocop", "1.85.0"
-gem "rubocop-minitest", "0.38.2"
+gem "rubocop-minitest", "0.39.1"
 gem "rubocop-packaging", "0.6.0"
 gem "rubocop-performance", "1.26.1"
 gem "rubocop-rake", "0.7.1"