set artifacts dir

Author: dubloom

.gitlab/benchmarks.yml

@@ -39,6 +39,7 @@ check-big-regressions:
   tags: ["arch:amd64"]
   image: $BENCHMARKS_CI_IMAGE
   script:
+    - export ARTIFACTS_DIR="$(pwd)/reports"
     - cd reports && (git init && git remote add origin https://gitlab-ci-token:${CI_JOB_TOKEN}@gitlab.ddbuild.io/DataDog/benchmarking-platform && git pull origin dd-trace-cpp)
     - bp-runner bp-runner.fail-on-regression.yml --debug
   variables: