Update activesupport requirement from >= 6.0, < 7.2 to >= 6.0, < 7.3

Updates the requirements on [activesupport](https://github.com/rails/rails) to permit the latest version.
- [Release notes](https://github.com/rails/rails/releases)
- [Changelog](https://github.com/rails/rails/blob/v7.2.1/activesupport/CHANGELOG.md)
- [Commits](rails/rails@v6.0.0...v7.1.4)

---
updated-dependencies:
- dependency-name: activesupport
  dependency-type: direct:production
...

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

granite.gemspec

@@ -13,7 +13,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 2.6'
 
   s.add_runtime_dependency 'actionpack', '>= 6.0', '< 7.2'
-  s.add_runtime_dependency 'activesupport', '>= 6.0', '< 7.2'
+  s.add_runtime_dependency 'activesupport', '>= 6.0', '< 7.3'
   s.add_runtime_dependency 'granite-form', '>= 0.3.0'
   s.add_runtime_dependency 'memoist', '~> 0.16'
   s.add_runtime_dependency 'ruby2_keywords', '~> 0.0.5'