There's a closed pull request on the void-packages repository

qt6ct: qt6ct.sh should not set QT_QPA_PLATFORMTHEME=qt5ct
https://github.com/void-linux/void-packages/pull/40619

Description:
qt6ct.sh should not set QT_QPA_PLATFORMTHEME=qt5ct unconditionally because it is already set in qt5ct.sh conditionally.

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#### Testing the changes
- I tested the changes in this PR: **YES**

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#### Local build testing
- I built this PR locally for my native architecture, (x86_64-glibc)