[BUGFIX] Followup Bootstrap for Unit Tests

There was a typo in the environment variable
check which prevented it from being evaluated.

This change fixes that.

Releases: 6.2
Change-Id: I05798ab00805e7c035dcf4635cf32c0e207822d3
Reviewed-on: https://review.typo3.org/24716
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel