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 3.0. 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.

Author: george-ma

.github/workflows/build.yml

@@ -13,6 +13,8 @@ jobs:
         version:
           - 3.0
           - 3.1
+          - 3.2
+          - 3.3
     steps:
       - uses: actions/checkout@v2
       - name: Set up Ruby ${{ matrix.version }}

.rubocop.yml

@@ -5,7 +5,6 @@ require:
   - rubocop-sorbet
 
 AllCops:
-  TargetRubyVersion: 2.7
   NewCops: enable
   Exclude:
     - "sorbet/**/*"

.ruby-version

@@ -0,0 +1 @@
+3.0.6

dev.yml

@@ -3,7 +3,7 @@ name: shopify-api
 type: ruby
 
 up:
-  - ruby: 3.0.6
+  - ruby
   - bundler:
       gemfile: Gemfile