AppImage: use latest Mesa and libva.so.

Due to how libva's backwards compatibility is handled, we
should use the latest libva but let it use the host system's
hardware specific drivers.

.github/workflows/CI.yml

@@ -321,11 +321,17 @@ jobs:
           # allow newer gcc
           sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
 
-          # Use more recent Mesa drivers than the ones of the base OS.
-          # This includes libdrm*, libva*, libvdpau*, libgl*, libegl*,
-          # libwayland*, and more specifically the VA drivers for
-          # both Intel (iHD, i965) and AMD (r600, radeonsi).
-          sudo add-apt-repository ppa:kisak/turtle -y
+          # We need to use a libva that is at least as recent as the
+          # actual hardware specific drivers (e.g. radeonsi_drv_video.so)
+          # on the host system. The "kisak-mesa fresh" PPA tracks the
+          # latest point release of the upstream Mesa project. This
+          # should (hopefully) ensure that the AppImage is also compatible
+          # with rolling release distributions.
+          # The PPA pulls in updated versions of libdrm*, libva*, libvdpau*,
+          # libgl*, libegl*, libwayland* and the accompanying -dev packages.
+          # Not all of the actual libraries will make it to the AppImage
+          # due to linuxdeploy's blacklist.
+          sudo add-apt-repository ppa:kisak/kisak-mesa -y
 
           sudo apt-get install -y \
             build-essential \