fix mtests under Windows MSVC

[AntonioBL]

Fixes running of mtests under Windows, when compiled with MSVC.
The "workspaces" folder was missing for the new palette tests, and the executable used for scripting tests was searching for "workspaces" folder as well.
No changes in the mtest instructions.

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• [N/A] I created the test (mtest, vtest, script test) to verify the changes I made