scm: git: replace "write_attribute" at unit model test for database order consistency (#5357)

On Rails 3.0.11, "NoMethodError: private method `write_attribute'" error raises.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8899 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/repository_git_test.rb

@@ -211,9 +211,12 @@ class RepositoryGitTest < ActiveSupport::TestCase
       @project.reload
       assert_equal NUM_REV, @repository.changesets.count
       assert_not_nil @repository.extra_info
-      @repository.write_attribute(:extra_info, nil)
+      h = {}
+      h["heads"] = []
+      h["branches"] = {}
+      h["db_consistent"] = {}
+      @repository.merge_extra_info(h)
       @repository.save
-      assert_nil @repository.extra_info
       assert_equal NUM_REV, @repository.changesets.count
       @repository.fetch_changesets
       @project.reload