Remove enforcing uniqueness of build variables

app/models/ci/build.rb

@@ -268,7 +268,7 @@ module Ci
       variables += pipeline.pipeline_schedule.job_variables if pipeline.pipeline_schedule
       variables += persisted_environment_variables if environment
 
-      variables.reverse.uniq { |variable| variable.fetch(:key) }.reverse
+      variables
     end
 
     def features

spec/models/ci/build_spec.rb

@@ -1873,14 +1873,13 @@ describe Ci::Build do
         pipeline.variables.build(key: 'MYVAR', value: 'pipeline value')
       end
 
-      it 'removes duplicates and leaves the latest occurence' do
-        expect(subject.count { |variable| variable.fetch(:key) == 'MYVAR' })
-          .to be 1
-      end
-
       it 'overrides YAML variable using a pipeline variable' do
-        is_expected.not_to include(key: 'MYVAR', value: 'myvar', public: true)
-        is_expected.to include(key: 'MYVAR', value: 'pipeline value', public: false)
+        variables = subject.reverse.uniq { |variable| variable[:key] }.reverse
+
+        expect(variables)
+          .not_to include(key: 'MYVAR', value: 'myvar', public: true)
+        expect(variables)
+          .to include(key: 'MYVAR', value: 'pipeline value', public: false)
       end
     end