ci(tracer): make serverless test unrequired (#12121)

## Checklist
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## Reviewer Checklist
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changes
- Testing strategy adequately addresses listed risks
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[release branch maintenance
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.gitlab/benchmarks.yml

@@ -96,6 +96,7 @@ benchmark-serverless:
   tags: ["arch:amd64"]
   when: on_success
   needs: [ "benchmark-serverless-trigger" ]
+  allow_failure: true
   script:
     - git clone https://gitlab-ci-token:${CI_JOB_TOKEN}@gitlab.ddbuild.io/DataDog/serverless-tools.git ./serverless-tools && cd ./serverless-tools
     - ./ci/check_trigger_status.sh