Fix unstable CI uncaughtException test

[juergba]

Description

One of our CI tests is unstable and fails occasionally.

• it should fail while the runner is still active which resulted in an exitCode of 2 (number of failing tests).
• sometimes it fails too late, after the EVENT_RUN_END event when all tests have finished. Then it is caught by the uncaughtException handler and exits with exitCode of 7.

Since 2 (expected) !== 7 (actual) ==> the test fails.

Description of Change

We use process.nextTick() instead of setTimeout().

related #4103

[coveralls]

Coverage remained the same at 92.723% when pulling b1f5a69 on juergba/stable-CI into 2e816fe on master.