Flaky test: @opentelemetry/sdk-trace-base should have an entered time for event

[legendecas]

I've observed several failures on the same test case across different CI runs.

Link: https://github.com/open-telemetry/opentelemetry-js/runs/5060952073?check_suite_focus=true

lerna ERR! npm run test:browser exited 1 in '@opentelemetry/sdk-trace-base'
lerna ERR! npm run test:browser stdout:

> @opentelemetry/[email protected] test:browser
> nyc karma start --single-run

1) should have an entered time for event
     Span
     AssertionError: 124 === 123
    at Context.<anonymous> (test/browser/index-webpack.js:31938:16)

2) should have an entered time for event - 
     Span when 2nd param is "TimeInput" type
     AssertionError: 124 === 123
    at Context.<anonymous> (test/browser/index-webpack.js:31948:20)