Run schema dumper extensions without creating real extensions

There is no need to create the extension in the database just to test if
it's dumped, we can stub that instead.

activerecord/test/cases/schema_dumper_test.rb

@@ -1,6 +1,5 @@
 require "cases/helper"
 
-
 class SchemaDumperTest < ActiveRecord::TestCase
   def setup
     super
@@ -233,19 +232,13 @@ def test_schema_dump_includes_decimal_options
   if current_adapter?(:PostgreSQLAdapter)
     def test_schema_dump_includes_extensions
       connection = ActiveRecord::Base.connection
-      return skip unless connection.supports_extensions?
-      unless connection.extension_enabled?('hstore')
-        connection.enable_extension 'hstore'
-      end
 
+      connection.stubs(:extensions).returns(['hstore'])
       output = standard_dump
       assert_match "# These are extensions that must be enabled", output
       assert_match %r{enable_extension "hstore"}, output
 
-      connection.extensions.each do |ext|
-        connection.disable_extension ext
-      end
-
+      connection.stubs(:extensions).returns([])
       output = standard_dump
       assert_no_match "# These are extensions that must be enabled", output
       assert_no_match %r{enable_extension}, output