Investigate test-timers-blocking-callback

[aqrln]

Unrelated failure of sequential/test-timers-blocking-callback on win2008r2 in #14773:

not ok 438 sequential/test-timers-blocking-callback
  ---
  duration_ms: 2.877
  severity: fail
  stack: |-
    assert.js:42
      throw new errors.AssertionError({
      ^
    
    AssertionError [ERR_ASSERTION]: false == true
        at blockingCallback (c:\workspace\node-test-binary-windows\RUN_SUBSET\1\VS_VERSION\vs2015\label\win2008r2\test\sequential\test-timers-blocking-callback.js:51:5)
        at ontimeout (timers.js:469:11)
        at tryOnTimeout (timers.js:304:5)
        at Timer.listOnTimeout (timers.js:264:5)
  ...

https://ci.nodejs.org/job/node-test-binary-windows/10459/RUN_SUBSET=1,VS_VERSION=vs2015,label=win2008r2/console

/cc @nodejs/testing @nodejs/platform-windows

[misterdjules]

test-timers-blocking-callback is unfortunately inherently flaky. See #9198 (comment) for a previous discussion on this topic.

[Trott]

Attempted mitigation: #14831