Downgrade nv-codec-headers and pin to version n11.x

[guihkx]

This allows hardware accelerated rendering on older - yet still supported - generations of NVIDIA GPUs (such as Kepler).

However, I'm not sure if this will negatively impact rendering on new NVIDIA GPUs, so if someone reading this has one, please give your feedback.

Thanks!

[flathubbot]

Started test build 60534

[flathubbot]

Build 60534 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/43168/org.kde.kdenlive.flatpakref

[travier]

Seems reasonable to me but I'll defer to kdenlive maintainers.

[jlskuz]

Can't say much about support for newer GPUs either so let's merge it

[flathubbot]

Started test build 65141

[flathubbot]

Build 65141 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/47782/org.kde.kdenlive.flatpakref