[BUGFIX] Environment check does not detect Windows OS

Obvious error. This code is now identical to ext:core
SystemEnvironmentBuilder.

Change-Id: Ic09c04bb8761ae6cb678d70118e4bcb94d2f7df9
Resolves: #46911
Releases: 6.1
Reviewed-on: https://review.typo3.org/19555
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn