[4.0] Fixing tests in media manager

[Hackwar]

The acceptance tests currently fail on the media manager tests, because a system message is overlapping the toolbar buttons, which Codeception is counting as a failure. This change adds an additional method that not only reads the system message, but also closes the dialog afterwards.

[Hackwar]

So just 9 commits later, this finally works. Please test and then lets get the tests working again for those other PRs...

[richard67]

I have tested this item ✅ successfully on d1326ab

Logs of system tests in drone look complete, i.e. no tests missing compared to the past when tests were successful.

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[HLeithner]

Thanks