[3.13] gh-132185: Speed up expanduser() test with large password database (GH-132231) (GH-132443)

Use only a limited number of randomly selected entries.
(cherry picked from commit 842ab815177549b9d4bec576d8f2c8f240b63506)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>