Intermittent test case failure

Bug Report

Current Behavior
A clear and concise description of the behavior.

One of test is failing intermittently on CI like below:

1) Observable
       should handle sync errors within a test scheduler:
     AssertionError: 
Expected 
	{"frame":0,"notification":{"kind":"E","error":{"name":"RangeError","message":"Maximum call stack size exceeded"}}}
	
to deep equal 

      at TestScheduler.observableMatcher [as assertDeepEqual] (dist/spec/helpers/observableMatcher.js:42:14)
          -> /home/runner/work/rxjs/rxjs/spec/helpers/observableMatcher.ts:45:10
      at /home/runner/work/rxjs/rxjs/dist/src/internal/testing/TestScheduler.js:183:23
          -> /home/runner/work/rxjs/rxjs/src/internal/testing/TestScheduler.ts:216:14
      at Array.filter (<anonymous>)
      at TestScheduler.flush (dist/src/internal/testing/TestScheduler.js:181:43)

Expected behavior
A clear and concise description of what you expected to happen (or code).

Reproduction

** Please provide repro code does not involves framework, or other setups to address this bug is specific to rxjs core **

• REPL or Repo link:
  (you can use https://stackblitz.com/ to create one to attach here)

var your => (code) => here;

Environment

• Runtime: [e.g. Node v${x}, Chrome v${x}]
• RxJS version:
• (If bug is related) Loader, build configuration: [e.g webpack, angular-cli version, config]

Possible Solution

Additional context/Screenshots
Add any other context about the problem here. If applicable, add screenshots to help explain.

Start with the Observable test named "should handle sync errors within a test scheduler" and inspect spec/helpers/observableMatcher.ts alongside src/internal/testing/TestScheduler.ts. Reproduce the intermittent CI failure and determine why the expected result becomes a RangeError; done means the test passes reliably without the stack overflow.