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.

.github/workflows/build.yml

@@ -9,7 +9,7 @@ jobs:
     name: Ruby ${{ matrix.version }}
     strategy:
       matrix:
-        version: [2.5.0, 2.7.1]
+        version: ['2.7', '3.0', '3.1', '3.2', '3.3']
 
     steps:
       - uses: actions/checkout@v2

.gitignore

@@ -1,2 +1 @@
 pkg/*
-Gemfile.lock

.ruby-version

@@ -0,0 +1 @@
+2.7.5

Gemfile.lock

@@ -0,0 +1,100 @@
+GIT
+  remote: https://github.com/chrisk/fakeweb.git
+  revision: 2b08c1ff2714ec13a12f3497d67fcefce95c2cbe
+  specs:
+    fakeweb (1.3.0)
+
+PATH
+  remote: .
+  specs:
+    omniauth-shopify-oauth2 (2.4.0)
+      activesupport
+      omniauth-oauth2 (~> 1.5)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (7.1.3.2)
+      base64
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      connection_pool (>= 2.2.5)
+      drb
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      mutex_m
+      tzinfo (~> 2.0)
+    base64 (0.2.0)
+    bigdecimal (3.1.7)
+    concurrent-ruby (1.2.3)
+    connection_pool (2.4.1)
+    diff-lcs (1.5.1)
+    drb (2.2.1)
+    faraday (2.8.1)
+      base64
+      faraday-net_http (>= 2.0, < 3.1)
+      ruby2_keywords (>= 0.0.4)
+    faraday-net_http (3.0.2)
+    hashie (5.0.0)
+    i18n (1.14.4)
+      concurrent-ruby (~> 1.0)
+    jwt (2.8.1)
+      base64
+    minitest (5.22.3)
+    multi_xml (0.6.0)
+    mutex_m (0.2.0)
+    oauth2 (2.0.9)
+      faraday (>= 0.17.3, < 3.0)
+      jwt (>= 1.0, < 3.0)
+      multi_xml (~> 0.5)
+      rack (>= 1.2, < 4)
+      snaky_hash (~> 2.0)
+      version_gem (~> 1.1)
+    omniauth (2.1.2)
+      hashie (>= 3.4.6)
+      rack (>= 2.2.3)
+      rack-protection
+    omniauth-oauth2 (1.8.0)
+      oauth2 (>= 1.4, < 3)
+      omniauth (~> 2.0)
+    rack (3.0.10)
+    rack-protection (3.0.6)
+      rack
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
+    rake (13.2.0)
+    rspec (3.9.0)
+      rspec-core (~> 3.9.0)
+      rspec-expectations (~> 3.9.0)
+      rspec-mocks (~> 3.9.0)
+    rspec-core (3.9.3)
+      rspec-support (~> 3.9.3)
+    rspec-expectations (3.9.4)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.9.0)
+    rspec-mocks (3.9.1)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.9.0)
+    rspec-support (3.9.4)
+    ruby2_keywords (0.0.5)
+    snaky_hash (2.0.1)
+      hashie
+      version_gem (~> 1.1, >= 1.1.1)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
+    version_gem (1.1.4)
+
+PLATFORMS
+  arm64-darwin-21
+  x86_64-linux
+
+DEPENDENCIES
+  fakeweb!
+  minitest (~> 5.6)
+  omniauth-shopify-oauth2!
+  rack-session (~> 2.0)
+  rake
+  rspec (~> 3.9.0)
+
+BUNDLED WITH
+   2.4.18

omniauth-shopify-oauth2.gemspec

@@ -17,7 +17,7 @@ Gem::Specification.new do |s|
   s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
   s.executables   = `git ls-files -- bin/*`.split("\n").map { |f| File.basename(f) }
   s.require_paths = ['lib']
-  s.required_ruby_version = '>= 2.1.9'
+  s.required_ruby_version = '>= 2.7'
 
   s.add_runtime_dependency 'omniauth-oauth2', '~> 1.5'
   s.add_runtime_dependency 'activesupport'