Centralize Ruby Version to .ruby-version

The `.ruby-version` file is the ecosystem standard for defining a Ruby version.  This PR adds the `.ruby-version` file, ensures a `required_ruby_version` is set, and removes all other references to Ruby in this repository, aligning it with the standard.
> [!IMPORTANT]
> Please verify the following before merging:

Verify that the changes in the PR meets the following requirements or adjust manually to make it compliant:
  - [ ] `.ruby-version` file is present with the correct Ruby version defined
  - [ ] A `required_ruby_version` in your gemspec is set
  - [ ] There is no Ruby version present in the  `dev.yml` Ruby task (before: `- ruby: x.x.x`, after: `- ruby`)
  - [ ] There is no Ruby version/requirement referenced in the `Gemfile` (no lines with `ruby  <some-version>`)
  - [ ] A `Gemfile.lock` is built with the defined Ruby version
  - [ ] The version of Rubocop installed is 1.61.0 or greater
  - [ ] There is no `TargetRubyVersion` defined  in `rubocop.yml` (reads from  `required_ruby_version` on Rubocop 1.61.0)
  - [ ] There is no Ruby argument  present in  `ruby/setup-ruby` Github Actions that do **not**  run on a Ruby matrix (no lines with `ruby-version: “x.x”`)

To establish consistency, the `required_ruby_version` is set to 2.7. If you think that another version is a better fit, please make the applicable changes.

Please merge this PR if it looks good, this PR will be addressed if there isn't any activity after 4 weeks.

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, 3.1, 3.3]
+        ruby: [2.7, 3.0, 3.1, 3.2, 3.3]
         graphql_version: ['~> 1.12.18', '~> 1.13', '~> 2.0']
         include:
           - ruby: 2.4

.rubocop.yml

@@ -6,6 +6,5 @@ inherit_from:
 
 AllCops:
   SuggestExtensions: false
-  TargetRubyVersion: 2.7
   Exclude:
     - vendor/**/*

Gemfile

@@ -4,6 +4,6 @@ gemspec
 
 gem 'graphql', ENV['GRAPHQL_VERSION'] if ENV['GRAPHQL_VERSION']
 if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.4.0')
-  gem 'rubocop', '~> 1.12.0', require: false
+  gem 'rubocop', '~> 1.61.0', require: false
   gem "rubocop-shopify", '~> 1.0.7', require: false
 end

graphql-batch.gemspec

@@ -10,6 +10,8 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/Shopify/graphql-batch"
   spec.license       = "MIT"
 
+  spec.required_ruby_version = ">= 2.7"
+
   spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }