Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Fixes #19646

What changes did you make? (Give an overview)

Updated isSerializable (lib/shared/serialization.js) to not cause a stack overflow error when the passed object has circular references, and in that case return false because objects with circular references are not JSON-serializable.

Also updated freezeDeeply (in lib/rule-tester/rule-tester.js) to to not cause a stack overflow error when the passed object has circular references.

Is there anything you'd like reviewers to focus on?

This is a very edge case, so I was more concerned if it would affect performance. By my performance testing, which was to run all core rules tests, it doesn't seem to significantly affect execution time.

Before:

$ time node node_modules/mocha/bin/_mocha -R min "tests/lib/rules/*.js"


  31860 passing (21s)


real    0m22.923s
user    0m0.015s 
sys     0m0.045s 

After:

$ time node node_modules/mocha/bin/_mocha -R min "tests/lib/rules/*.js"


  31860 passing (21s)


real    0m22.946s
user    0m0.000s 
sys     0m0.030s