Change cache index delimiter to character not recognizable as variable part

app/models/ci/build.rb

@@ -467,7 +467,7 @@ module Ci
 
       if cache && project.jobs_cache_index
         cache = cache.merge(
-          key: "#{cache[:key]}_#{project.jobs_cache_index}")
+          key: "#{cache[:key]}-#{project.jobs_cache_index}")
       end
 
       [cache]

spec/models/ci/build_spec.rb

@@ -277,7 +277,7 @@ describe Ci::Build do
           allow_any_instance_of(Project).to receive(:jobs_cache_index).and_return(1)
         end
 
-        it { is_expected.to be_an(Array).and all(include(key: "key_1")) }
+        it { is_expected.to be_an(Array).and all(include(key: "key-1")) }
       end
 
       context 'when project does not have jobs_cache_index' do