Deprecate GoodJob.v4_ready?

If you're reading this deprecation you're already all good (:

lib/good_job.rb

@@ -269,6 +269,10 @@ def self.perform_inline(queue_string = "*", limit: nil)
   # Tests whether GoodJob can be safely upgraded to v4
   # @return [Boolean]
   def self.v4_ready?
+    GoodJob.deprecator.warn(<<~MSG)
+      Calling `GoodJob.v4_ready?` is deprecated and will be removed in GoodJob v5.
+      If you are reading this deprecation you are already on v4.
+    MSG
     true
   end
 

spec/lib/good_job_spec.rb

@@ -165,7 +165,9 @@ def perform(succeed: true)
 
   describe '#v4_ready?' do
     it "is true" do
+      allow(GoodJob.deprecator).to receive(:warn)
       expect(described_class.v4_ready?).to eq true
+      expect(GoodJob.deprecator).to have_received(:warn)
     end
   end
 end