DEV: Upgrade Rails to 6.1.3.1 (#12688)

Rails 6.1.3.1 deprecates a few API and has some internal changes that break our tests suite, so this commit fixes all the deprecations and errors and now Discourse should be fully compatible with Rails 6.1.3.1. We also have a new release of the rails_failover gem that's compatible with Rails 6.1.3.1.

spec/requests/application_controller_spec.rb

@@ -282,9 +282,7 @@ RSpec.describe ApplicationController do
       get "/search/query.json", params: { trem: "misspelled term" }
 
       expect(response.status).to eq(400)
-      expect(response.parsed_body).to eq(
-        "errors" => ["param is missing or the value is empty: term"]
-      )
+      expect(response.parsed_body["errors"].first).to include("param is missing or the value is empty: term")
     end
   end