[backport#13551] tests: Fix incorrect documentation for test case cuckoocache_hit_rate_ok

Summary:
Fix incorrect documentation for test case cuckoocache_hit_rate_ok (practicalswift)

https://github.com/bitcoin/bitcoin/pull/13551/commits/ea49e06c8211d8642a52a4b120c7b3d41836ea03

Backport of Core PR13551

Test Plan:

none

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7276