[TASK] Add missing unit tests for TcaMigration class

The method migrateIconfileRelativePathOrFilenameOnlyToExtReference()
of class TcaMigration misses unit tests.

Change-Id: I598e1729600fe184ecc3d32afbe78f91d2c2afcb
Resolves: #69978
Relates: #69754
Releases: master
Reviewed-on: http://review.typo3.org/43439


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>