test: move inspector-stress-http to sequential

test-inspector-stress-http launches 100 simultaneous http requests. It
is unreliable in the parallel directory (as can be seen with
tools/test.py and sufficiently high -j and --repeat values). Move to
sequential.

PR-URL: #21227
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: Trott