chore: update ruby testings to reflect supported rubies

chore: explicity set supported ruby versions

.github/workflows/ruby.yml

@@ -6,7 +6,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-latest ]
-        ruby: [ '2.6', '2.7', '3.0', '3.1', '3.2' ]
+        ruby: [ '3.0', '3.1', '3.2', '3.3' ]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v3

tracking_number.gemspec

@@ -9,6 +9,7 @@ Gem::Specification.new do |s|
   s.version = TrackingNumber::VERSION
   s.platform = Gem::Platform::RUBY
   s.required_rubygems_version = Gem::Requirement.new('>= 0') if s.respond_to? :required_rubygems_version=
+  s.required_ruby_version = Gem::Requirement.new('>= 3.0.0')
   s.authors = ['Jeff Keen']
   s.description = "This gem identifies valid tracking numbers and the service they're associated with. It can also tell you a little bit about the package purely from the number—there's quite a bit of info tucked away into those numbers, it turns out."
   s.email = 'jeff@keen.me'