LU-17733 tests: sanity test_45 fix dirty count

LU-17733 tests: sanity test_45 fix dirty count

Change test comparisons to ge (>=) instead of gt (>). A comment was
added identifying the race condition within the test related to the
completion of async io.  Also updated sync condition to check dirty
bytes after sync is equal to 0

Test-Parameters: testlist=sanity env=ONLY=45
Signed-off-by: Cyrus Ramavarapu <cramavarapu@microsoft.com>
Change-Id: I5826d82a16e20101a2eb8d415bdbde1b6bcc8d69
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54763
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>