Fix: packages_and_registries_spec.rb unstable blur trigger issue

What does this MR do?

• Fix the issue which caused blur event not triggering for JH when content-wrapper has min-height: calc() set which covers the entire body

The original issue can be found JH issues 169

cc @wortschi

Background:

In JH, we introduced customized style rule for content-wrapper with min-height for positioning the global footer (which means the content-wrapper will completely cover body element, in this case the test case used find('body).click to trigger blur event which is blocked by content-wrapper(hypothetically), it was just somehow unable to trigger the event by clicking the body event. So that we use blur event on the input box.

NOTE: The test runs completely ok locally, no idea why inside CI container it just fails.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

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