Do not validate ref for release

lib/gitlab/ci/config/entry/release.rb

@@ -42,13 +42,6 @@ module Gitlab
                 errors.add(:released_at, "must be a valid datetime")
               end
             end
-            validate do
-              next unless config[:ref]
-
-              unless Commit.reference_valid?(config[:ref])
-                errors.add(:ref, "must be a valid ref")
-              end
-            end
           end
 
           def value

spec/lib/gitlab/ci/config/entry/release_spec.rb

@@ -192,12 +192,6 @@ RSpec.describe Gitlab::Ci::Config::Entry::Release do
           it_behaves_like 'reports error', 'release released at must be a valid datetime'
         end
 
-        context 'when `ref` is not valid' do
-          let(:config) { { ref: 'ABC123' } }
-
-          it_behaves_like 'reports error', 'release ref must be a valid ref'
-        end
-
         context 'when `milestones` is not an array of strings' do
           let(:config) { { milestones: [1, 2, 3] } }
 
@@ -210,12 +204,6 @@ RSpec.describe Gitlab::Ci::Config::Entry::Release do
           it_behaves_like 'reports error', 'release released at must be a valid datetime'
         end
 
-        context 'when `ref` is not valid' do
-          let(:config) { { ref: 'ABC123' } }
-
-          it_behaves_like 'reports error', 'release ref must be a valid ref'
-        end
-
         context 'when `milestones` is not an array of strings' do
           let(:config) { { milestones: [1, 2, 3] } }