[BUGFIX] Failing FAL unit test

Using 0042 as create mask for files in unit test from issue #49029
triggers a warning and lets the test fail when the test file is
removed again. Relaxing the create mask to 0642 solves the issue.

Change-Id: I1bfdb344df5160505d853a725584c2a98f30494b
Resolves: #49296
Related: #49029
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/21544
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn