ci: adjust performance gate warning to 1% for low stddev scenarios (#6626)

Author: rochdev

.gitlab/benchmarks/bp-runner.fail-on-breach.yml

@@ -12,12 +12,12 @@ experiments:
           - name: normal_operation/only-tracing
             thresholds:
               - threshold: agg_http_req_duration_p50 < 2 ms
-                warning_range: 3
+                warning_range: 1
               - agg_http_req_duration_p99 < 15 ms
           - name: normal_operation/only-tracing-with-runtime-metrics-enabled
             thresholds:
               - threshold: agg_http_req_duration_p50 < 2 ms
-                warning_range: 3
+                warning_range: 1
               - agg_http_req_duration_p99 < 16 ms
           - name: high_load/only-tracing
             thresholds: