[Bug] [Flaky test]: CanceledTasksDoNotLogMSB4181 unit test is unreliable

[jrdodds]

Issue Description

Unit test Microsoft.Build.UnitTests.BackEnd.TaskBuilder_Tests.CanceledTasksDoNotLogMSB4181 failed on a PR build.

Shouldly.ShouldAssertException : logger.WarningCount
    should be
1
    but was
0

The test includes a Thread.Sleep call.

Steps to Reproduce

The issue was found when running the set of unit tests during a PR build but it appears to be a threading race condition and the test doesn't consistently break.

Expected Behavior

The test should pass for the PR build where it failed.

Actual Behavior

The test failed for Windows Core while passing for the other type of builds within the PR build.

Analysis

Related to:
#9277
#9100

A search in the repo shows that Thread.Sleep appears 163 times in 32 files. About 22 of the files appear to be unit tests or test support.

Versions & Configurations

No response