record the cpu usage in a gitignored directory

src/ci/scripts/collect-cpu-stats.sh

@@ -6,4 +6,5 @@
 set -euo pipefail
 IFS=$'\n\t'
 
-python3 src/ci/cpu-usage-over-time.py &> cpu-usage.csv &
+mkdir -p build
+python3 src/ci/cpu-usage-over-time.py &> build/cpu-usage.csv &

src/ci/scripts/upload-artifacts.sh

@@ -23,7 +23,7 @@ if [[ "${DEPLOY-0}" -eq "1" ]] || [[ "${DEPLOY_ALT-0}" -eq "1" ]]; then
 fi
 
 # CPU usage statistics.
-cp cpu-usage.csv "${upload_dir}/cpu-${CI_JOB_NAME}.csv"
+cp build/cpu-usage.csv "${upload_dir}/cpu-${CI_JOB_NAME}.csv"
 
 # Build metrics generated by x.py.
 cp "${build_dir}/metrics.json" "${upload_dir}/metrics-${CI_JOB_NAME}.json"