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 <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Jon Moss <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>

Author: Trott