LU-16778 tests: sanity-quota_75 fix

LU-16778 tests: sanity-quota_75 fix

Change conf=fsync to oflag=direct to avoid
cache write.

Test-Parameters: trivial testlist=sanity-quota env=ONLY=75,ONLY_REPEAT=100
Signed-off-by: Sergey Cheremencev <scherementsev@ddn.com>
Change-Id: Iff04bac63f772dc2d0d0ad765d210b2539fbe33e
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51158
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>