fix(file source): Increase sleep interval in the tests for file source

[ghost]

On some occurrences the sleep interval in tests for file source turns out to be too small, which makes the tests fail. This PR increases it 10x to make sure that that interval is large enough for all test platforms.

Ref #1054 (comment)

[binarylogic]

😦 I wish we could deterministicly wait, but whatever works for now.

[lukesteensen]

@binarylogic I'm open to any ideas you have on how to improve these tests 😉

[binarylogic]

The only idea I have is to offer a function we can call that would perform the file read iteration and block. This way the function could be called instead of waiting an arbitrary amount of time. Example pseudo code:

file.write('some content')
file_source.refresh() // blocks until done
// make test assertion

Would that be possible?