TaskHelpers: Enable git protocol v2

Doing git-fetch(1) to get an object by ID might fail when the git
repository is a shallow clone. To make sure, even older versions of, git
is able to pull those in, configure the repository to use git protocol
version 2.

lib/gitlab/task_helpers.rb

@@ -190,6 +190,9 @@ module Gitlab
     end
 
     def checkout_version(version, target_dir)
+      # Explicitly setting the git protocol version to v2 allows older Git binaries
+      # to do have a shallow clone obtain objects by object ID.
+      run_command!(%W[#{Gitlab.config.git.bin_path} -C #{target_dir} config protocol.version 2])
       run_command!(%W[#{Gitlab.config.git.bin_path} -C #{target_dir} fetch --quiet origin #{version}])
       run_command!(%W[#{Gitlab.config.git.bin_path} -C #{target_dir} checkout -f --quiet FETCH_HEAD --])
     end

spec/tasks/gitlab/task_helpers_spec.rb

@@ -71,6 +71,8 @@ RSpec.describe Gitlab::TaskHelpers do
 
   describe '#checkout_version' do
     it 'clones the repo in the target dir' do
+      expect(subject)
+        .to receive(:run_command!).with(%W[#{Gitlab.config.git.bin_path} -C #{clone_path} config protocol.version 2])
       expect(subject)
         .to receive(:run_command!).with(%W[#{Gitlab.config.git.bin_path} -C #{clone_path} fetch --quiet origin #{tag}])
       expect(subject)