The tests start to show flakyness on Linux in 5.10 (rowCount() check
failing). This seems to point to a race condition between the files
showing up and the file system watchers of QFileSystemModel starting.
To fix this, close the file and wait until it shows up in the directory
before pointing the QFileSystemModel to it. The tests then no longer
rely on the file system watchers.
Change-Id: I39cffb4cacf6843e8e4180efb405345307c78dd8
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>