LU-16608 tests: Reduce lock count in 255c

LU-16608 tests: Reduce lock count in 255c

Similar to LU-10443/LU-10136, test 255c is failing due to
lock reclamation during the test, this time on GK testing.

Reducing the lock count in the test from 500 to 100 should
dramatically reduce the frequency of failures, and is
still a good test.

Test-parameters: trivial testlist=sanity env=ONLY=255c,ONLY_REPEAT=100
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I47c9a60c8425b73c53093bae34995c08c8278f2b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50174
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Deiter <alex.deiter@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>