Bump Rugged to 0.28.0

This version bump makes things consistent between Gitaly and
fixes a significant number of bugs:
https://github.com/libgit2/libgit2/releases

This also decreases disk space of Omnibus builds by ~30 MB.

There is also a workaround for
https://github.com/libgit2/rugged/issues/785. If Gitaly or another
process changes .gitconfig while Rugged has the file loaded,
Rugged::Repository#each_key will report stale values unless a lookup is
done first.

This bug only manifests in a spec because we are using both Gitaly and
Rugged at the same time there, and we normally don't use Rugged in the
CE/EE code in this way.

Gemfile

@@ -18,7 +18,7 @@ gem 'gitlab-default_value_for', '~> 3.1.1', require: 'default_value_for'
 gem 'mysql2', '~> 0.4.10', group: :mysql
 gem 'pg', '~> 1.1', group: :postgres
 
-gem 'rugged', '~> 0.27'
+gem 'rugged', '~> 0.28'
 gem 'grape-path-helpers', '~> 1.0'
 
 gem 'faraday', '~> 0.12'

Gemfile.lock

@@ -784,7 +784,7 @@ GEM
     rubyntlm (0.6.2)
     rubypants (0.2.0)
     rubyzip (1.2.2)
-    rugged (0.27.5)
+    rugged (0.28.0)
     safe_yaml (1.0.4)
     sanitize (4.6.6)
       crass (~> 1.0.2)
@@ -1134,7 +1134,7 @@ DEPENDENCIES
   ruby-progressbar
   ruby_parser (~> 3.8)
   rubyzip (~> 1.2.2)
-  rugged (~> 0.27)
+  rugged (~> 0.28)
   sanitize (~> 4.6)
   sass (~> 3.5)
   sass-rails (~> 5.0.6)

spec/lib/gitlab/git/repository_spec.rb

@@ -1688,6 +1688,11 @@ describe Gitlab::Git::Repository, :seed_helper do
 
       expect(repository.delete_config(*%w[does.not.exist test.foo1 test.foo2])).to be_nil
 
+      # Workaround for https://github.com/libgit2/rugged/issues/785: If
+      # Gitaly changes .gitconfig while Rugged has the file loaded
+      # Rugged::Repository#each_key will report stale values unless a
+      # lookup is done first.
+      expect(repository_rugged.config['test.foo1']).to be_nil
       config_keys = repository_rugged.config.each_key.to_a
       expect(config_keys).not_to include('test.foo1')
       expect(config_keys).not_to include('test.foo2')