Keep different code in custom branch in dummy repo

This doesn't affect the outcome of the test, but it makes the `git
commit` command inside `update_git` not fail because of not having
anything to commit.

bundler/spec/install/gemfile/git_spec.rb

@@ -232,7 +232,7 @@
 
       # want to ensure we don't fallback to HEAD
       update_git "foo", :path => lib_path("foo-1.0"), :branch => "rando" do |s|
-        s.write("lib/foo.rb", "raise 'FAIL'")
+        s.write("lib/foo.rb", "raise 'FAIL_FROM_RANDO'")
       end
 
       install_gemfile <<-G
@@ -268,7 +268,7 @@
 
       # want to ensure we don't fallback to HEAD
       update_git "foo", :path => lib_path("foo-1.0"), :branch => "rando" do |s|
-        s.write("lib/foo.rb", "raise 'FAIL'")
+        s.write("lib/foo.rb", "raise 'FAIL_FROM_RANDO'")
       end
 
       install_gemfile <<-G