Tweak list pipeline jobs API threshold

Smaller environments like 1k have worse TTFB results. The MR is to tweak the threshold.

* Environment:                1k
* Environment Version:        14.5.0-pre `7506b083594`
* Option:                     60s_20rps
* Date:                       2021-11-17
* Run Time:                   1h 25m 58.06s (Start: 04:23:54 UTC, End: 05:49:52 UTC)
* GPT Version:                v2.9.0
❯ Overall Results Score: 98.9%
NAME                                                     | RPS  | RPS RESULT         | TTFB AVG  | TTFB P90             | REQ STATUS     | RESULT  
---------------------------------------------------------|------|--------------------|-----------|----------------------|----------------|---------
api_v4_projects_project_pipelines_pipeline_jobs          | 20/s | 18.75/s (>16.00/s) | 864.38ms  | 1126.60ms (<600ms)   | 100.00% (>99%) | FAILED¹²