UI: Fix Linux base folder location

[Penwy]

Description

This changes the BASE_FOLDER to be .. instead of ../.. on linux.

Motivation and Context

On linux, the binaries are directly in the bin folder, so one level above the base folder. As such setting BASE_FOLDER to ../.. caused the config folder to be created one level below where it should be.

How Has This Been Tested?

Launched OBS, checked that the config folder was created correctly.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Re-targeting this to release/31.0. The change has been ported to master in #11622.