Update minitest requirement from ~> 5.0 to ~> 6.0

Updates the requirements on [minitest](https://github.com/minitest/minitest) to permit the latest version.
- [Changelog](https://github.com/minitest/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.0.0...v6.0.1)

---
updated-dependencies:
- dependency-name: minitest
  dependency-version: 6.0.1
  dependency-type: direct:development
...

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

Author: dependabot[bot]

activeagent.gemspec

@@ -37,7 +37,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "ostruct"
   spec.add_development_dependency "puma"
   spec.add_development_dependency "sqlite3"
-  spec.add_development_dependency "minitest", "~> 5.0"
+  spec.add_development_dependency "minitest", "~> 6.0"
   spec.add_development_dependency "vcr"
   spec.add_development_dependency "webmock"