[BUGFIX] Better mocking in BackendUtility::viewOnClick test

BackendUtility::viewOnClick() provides a hook to manipulate the
generated URL. ext:workspaces uses this. The patch adapts a
viewOnClick() test to unset possible registered hooks and prevents
unrelated code from messing with the test.

Change-Id: I4977575446bf898224583010ae7a2d34e145e147
Resolves: #52813
Releases: 6.2
Reviewed-on: https://review.typo3.org/24748
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn