test: improve readline coverage to check end and clear keys

[chiiia12]

I improved test coverage for readline. I found some key tests are missing. This PR will improve coverage

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

N/A

[yosuke-furukawa]

Hello, @nodejs/collaborators .
I am teaching about how to contribute node.js in my office (like code-and-learn) .
She would like to contribute improvement some tests. please review.

[hiroppy]

Hello, chiiia12 and Yosuke!
Thank you for your contribution 😘
This is LGTM but I submitted the same tests before. #10772

[chiiia12]

Hello, abouthiroppy!
Thanks for your review!!