[BUGFIX] Move functional test case to functional folder

ext:core File/ExtendedFileUtilityTest unit test is not really
a unit test, but more a functional test case since it does no
mocking at all and writes data directly to database.
The test case has side effects and is move to the functional
section for now.

Resolves: #49746
Releases: 6.2, 6.1, 6.0
Change-Id: I3f3917f0800a9492b01676bf2b67e81eea1ae16f
Reviewed-on: https://review.typo3.org/22051
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn