gems: update async requirement from ~> 1.31.0 to >= 1.31, < 2.36

Updates the requirements on [async](https://github.com/socketry/async) to permit the latest version.
- [Release notes](https://github.com/socketry/async/releases)
- [Changelog](https://github.com/socketry/async/blob/main/releases.md)
- [Commits](https://github.com/socketry/async/compare/v1.31.0...v2.35.0)

---
updated-dependencies:
- dependency-name: async
  dependency-version: 2.35.0
  dependency-type: direct:production
...

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

dyndnsd.gemspec

@@ -27,7 +27,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 3.0'
 
-  s.add_dependency 'async', '~> 1.31.0'
+  s.add_dependency 'async', '>= 1.31', '< 2.36'
   s.add_dependency 'async-dns', '~> 1.3.0'
   s.add_dependency 'base64', '~> 0.2.0' # needed for async
   s.add_dependency 'logger', '>= 1.6', '< 1.8'