s3: tests: Slight tweak to the force-close share test.

s3: tests: Slight tweak to the force-close share test.

Turns out on a fast desktop machine 10MB is too small,
and by the time we've done the 'sleep 1' to make sure
the smbclient got scheduled and started processing
the 'put' command, it's already done.

Tweak the file size to be 20MB from 10MB. 10MB
seems to work reliably on gitlab-ci and on
sn-devel, but making the put size 20MB makes
sure it's still in flight when we force-close
the share, even on a fast desktop box. 20MB
shouldn't be too burdonsome even on ci VM's.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14301

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>