Handle Rack 3.2 unprocessable_{entity,content}

Using `unprocessable_entity` will emit a warning on Rack 3.2.
There have been various PRs in the past for this:
* rails#52252
* rails#52192
* rails#52087
* rails#52097

This to me seems like the least invasive change and is also how headers are currently handled.

Author: Earlopain

actionmailbox/app/controllers/action_mailbox/ingresses/mandrill/inbound_emails_controller.rb

@@ -22,7 +22,7 @@ def create
       head :ok
     rescue JSON::ParserError => error
       logger.error error.message
-      head :unprocessable_entity
+      head ActionDispatch::Constants::UNPROCESSABLE_CONTENT
     end
 
     def health_check

actionmailbox/app/controllers/action_mailbox/ingresses/postmark/inbound_emails_controller.rb

@@ -57,7 +57,7 @@ def create
         When configuring your Postmark inbound webhook, be sure to check the box
         labeled "Include raw email content in JSON payload".
       MESSAGE
-      head :unprocessable_entity
+      head ActionDispatch::Constants::UNPROCESSABLE_CONTENT
     end
 
     private

actionmailbox/app/controllers/action_mailbox/ingresses/relay/inbound_emails_controller.rb

@@ -55,7 +55,7 @@ def create
       if request.body
         ActionMailbox::InboundEmail.create_and_extract_message_id! request.body.read
       else
-        head :unprocessable_entity
+        head ActionDispatch::Constants::UNPROCESSABLE_CONTENT
       end
     end
 

actionmailbox/app/controllers/action_mailbox/ingresses/sendgrid/inbound_emails_controller.rb

@@ -52,7 +52,7 @@ def create
       ActionMailbox::InboundEmail.create_and_extract_message_id! mail
     rescue JSON::ParserError => error
       logger.error error.message
-      head :unprocessable_entity
+      head ActionDispatch::Constants::UNPROCESSABLE_CONTENT
     end
 
     private

actionmailbox/test/controllers/ingresses/postmark/inbound_emails_controller_test.rb

@@ -53,7 +53,7 @@ class ActionMailbox::Ingresses::Postmark::InboundEmailsControllerTest < ActionDi
         headers: { authorization: credentials }, params: { From: "[email protected]" }
     end
 
-    assert_response :unprocessable_entity
+    assert_response ActionDispatch::Constants::UNPROCESSABLE_CONTENT
   end
 
   test "rejecting an unauthorized inbound email from Postmark" do

actionmailbox/test/controllers/ingresses/relay/inbound_emails_controller_test.rb

@@ -37,7 +37,7 @@ class ActionMailbox::Ingresses::Relay::InboundEmailsControllerTest < ActionDispa
         env: { "rack.input" => nil }
     end
 
-    assert_response :unprocessable_entity
+    assert_response ActionDispatch::Constants::UNPROCESSABLE_CONTENT
   end
 
   test "rejecting an unauthorized inbound email" do

actionpack/lib/action_dispatch/constants.rb

@@ -30,5 +30,11 @@ module Constants
       SERVER_TIMING = "server-timing"
       STRICT_TRANSPORT_SECURITY = "strict-transport-security"
     end
+
+    if Gem::Version.new(Rack::RELEASE) < Gem::Version.new("3.1")
+      UNPROCESSABLE_CONTENT = :unprocessable_entity
+    else
+      UNPROCESSABLE_CONTENT = :unprocessable_content
+    end
   end
 end

actionpack/lib/action_dispatch/middleware/exception_wrapper.rb

@@ -18,8 +18,8 @@ class ExceptionWrapper
       "ActionController::UnknownFormat"                    => :not_acceptable,
       "ActionDispatch::Http::MimeNegotiation::InvalidType" => :not_acceptable,
       "ActionController::MissingExactTemplate"             => :not_acceptable,
-      "ActionController::InvalidAuthenticityToken"         => :unprocessable_entity,
-      "ActionController::InvalidCrossOriginRequest"        => :unprocessable_entity,
+      "ActionController::InvalidAuthenticityToken"         => ActionDispatch::Constants::UNPROCESSABLE_CONTENT,
+      "ActionController::InvalidCrossOriginRequest"        => ActionDispatch::Constants::UNPROCESSABLE_CONTENT,
       "ActionDispatch::Http::Parameters::ParseError"       => :bad_request,
       "ActionController::BadRequest"                       => :bad_request,
       "ActionController::ParameterMissing"                 => :bad_request,

actionpack/test/controller/rescue_test.rb

@@ -147,7 +147,7 @@ def deny_access
     end
 
     def show_errors(exception)
-      head :unprocessable_entity
+      head ActionDispatch::Constants::UNPROCESSABLE_CONTENT
     end
 end
 
@@ -289,12 +289,12 @@ def test_block_rescue_handler_with_argument_as_string
 
   test "rescue when cause has more specific handler than wrapper" do
     get :exception_with_more_specific_handler_for_cause
-    assert_response :unprocessable_entity
+    assert_response ActionDispatch::Constants::UNPROCESSABLE_CONTENT
   end
 
   test "rescue when cause has handler, but wrapper doesn't" do
     get :exception_with_no_handler_for_wrapper
-    assert_response :unprocessable_entity
+    assert_response ActionDispatch::Constants::UNPROCESSABLE_CONTENT
   end
 
   test "can rescue a ParseError" do

actionpack/test/dispatch/debug_exceptions_test.rb

@@ -86,8 +86,6 @@ def call(env)
         raise ActionController::UnknownHttpMethod
       when "/not_implemented"
         raise ActionController::NotImplemented
-      when "/unprocessable_entity"
-        raise ActionController::InvalidAuthenticityToken
       when "/invalid_mimetype"
         raise ActionDispatch::Http::MimeNegotiation::InvalidType
       when "/not_found_original_exception"