Refactor gemfiles

We aren't using groups, so we can take a simpler approach by keeping runtime
dependencies in the gemspec, and everything else in Gemfile.

We can also use eval_gemfile to avoid repeating ourselves.

Instance variable approach based on Shopify/maintenance_tasks.

Gemfile

@@ -4,11 +4,14 @@ source "https://rubygems.org"
 
 gemspec
 
-group :deployment do
-  gem "rake"
-  gem "rubocop"
-end
+gem "bundler"
+gem "minitest"
+gem "rake"
+gem "rspec"
+gem "rubocop-shopify"
 
-group :test do
-  gem "rubocop-shopify"
+if defined?(@activesupport_gem_requirement) && @activesupport_gem_requirement
+  # causes Dependabot to ignore the next line
+  activesupport = "activesupport"
+  gem activesupport, @activesupport_gem_requirement
 end

Gemfile.lock

@@ -63,12 +63,11 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  bundler (>= 1.16)
+  bundler
   deprecation_toolkit!
-  minitest (~> 5.0)
+  minitest
   rake
-  rspec (~> 3.0)
-  rubocop
+  rspec
   rubocop-shopify
 
 BUNDLED WITH

deprecation_toolkit.gemspec

@@ -28,9 +28,4 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
 
   spec.add_runtime_dependency("activesupport", ">= 5.2")
-
-  spec.add_development_dependency("bundler", ">= 1.16")
-  spec.add_development_dependency("minitest", "~> 5.0")
-  spec.add_development_dependency("rake", "~> 10.0")
-  spec.add_development_dependency("rspec", "~> 3.0")
 end

gemfiles/activesupport_5.2.gemfile

@@ -1,12 +1,5 @@
 # frozen_string_literal: true
 
-source "https://rubygems.org"
+@activesupport_gem_requirement = "~> 5.2"
 
-gem "activesupport", "~> 5.2"
-
-group :deployment do
-  gem "rake"
-  gem "rubocop"
-end
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"

gemfiles/activesupport_6.0.gemfile

@@ -1,12 +1,5 @@
 # frozen_string_literal: true
 
-source "https://rubygems.org"
+@activesupport_gem_requirement = "~> 6.0"
 
-gem "activesupport", "~> 6.0"
-
-group :deployment do
-  gem "rake"
-  gem "rubocop"
-end
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"

gemfiles/activesupport_6.1.gemfile

@@ -1,12 +1,5 @@
 # frozen_string_literal: true
 
-source "https://rubygems.org"
+@activesupport_gem_requirement = "~> 6.1"
 
-gem "activesupport", "~> 6.1"
-
-group :deployment do
-  gem "rake"
-  gem "rubocop"
-end
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"

gemfiles/activesupport_7.0.gemfile

@@ -1,12 +1,5 @@
 # frozen_string_literal: true
 
-source "https://rubygems.org"
+@activesupport_gem_requirement = "~> 7.0"
 
-gem "activesupport", "~> 7.0"
-
-group :deployment do
-  gem "rake"
-  gem "rubocop"
-end
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"