Rails5 fix connection execute return integer instead of string

changelogs/unreleased/rails5-fix-db-check.yml

+---
+title: Rails5 fix connection execute return integer instead of string
+merge_request: 19901
+author: Jasper Maes
+type: fixed

lib/gitlab/health_checks/db_check.rb

@@ -17,7 +17,7 @@ module Gitlab
         def check
           catch_timeout 10.seconds do
             if Gitlab::Database.postgresql?
-              ActiveRecord::Base.connection.execute('SELECT 1 as ping')&.first&.[]('ping')
+              ActiveRecord::Base.connection.execute('SELECT 1 as ping')&.first&.[]('ping')&.to_s
             else
               ActiveRecord::Base.connection.execute('SELECT 1 as ping')&.first&.first&.to_s
             end