kbfs_ops_test: fix grammar in comment
kbfs_ops_test: fix grammar in comment

Suggested by songgao.

Issue: #16594

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client