Update runtime

[yakushabb]

Update out-of-date runtime versino to 6.6

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[flathubbot]

Started test build 117690

[flathubbot]

Build 117690 failed

[flathubbot]

Started test build 117696

[okias]

If you want, I can do the bump together with your patch (second open PR here).

[flathubbot]

Build 117696 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/100522/cz.cvut.edu.comparch.qtrvsim.flatpakref

[yakushabb]

@okias FYI

[okias]

Merged into #4 . Closing. Thank you!