Add X checker data for auto updates

[proletarius101]

• Add X checker data for auto updates
• Switch x264 to the stable branch which is updated but stable

[flathubbot]

Started test build 39757

[flathubbot]

Build 39757 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/38264/org.blender.Blender.flatpakref

[barthalion]

You really can't randomly bump x264 like that and hope ffmpeg will always like it.

[proletarius101]

Then that's removed

[flathubbot]

Started test build 39790

[flathubbot]

Build 39790 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/38293/org.blender.Blender.flatpakref

[proletarius101]

I still decide not to look into supporting aarch64 because the precompiled libs are only for x64 and needs some more work to support aarch64. But my contribution makes it easier to do

The switching to git will be submitted as another PR first