scm: git: use to_s for branches at model (#5501)

"scm.branches" will extend to have the revision for the branch.
no "to_s" will have a problem.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7653 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/repository/git.rb

@@ -129,7 +129,8 @@ class Repository::Git < Repository
       merge_extra_info(h)
       self.save
     end
-    scm_brs.each do |br|
+    scm_brs.each do |br1|
+      br = br1.to_s
       from_scmid = nil
       from_scmid = h["branches"][br]["last_scmid"] if h["branches"][br]
       h["branches"][br] ||= {}