flatpak: update KDE runtime to 6.8

This also switches to the Docker image provided and maintained by
Flathub collaborators through the 'flathub-infra' organization on
GitHub, because it looks better maintained at the moment.

Signed-off-by: guihkx <626206+guihkx@users.noreply.github.com>
(cherry picked from commit f6770a847a8419ef0b1acab30144077f745a48ee)

.github/workflows/build.yml

@@ -633,7 +633,7 @@ jobs:
   flatpak:
     runs-on: ubuntu-latest
     container:
-      image: bilelmoussaoui/flatpak-github-actions:kde-6.7
+      image: ghcr.io/flathub-infra/flatpak-github-actions:kde-6.8
       options: --privileged
     steps:
       - name: Checkout

flatpak/org.prismlauncher.PrismLauncher.yml

@@ -1,6 +1,6 @@
 id: org.prismlauncher.PrismLauncher
 runtime: org.kde.Platform
-runtime-version: '6.7'
+runtime-version: '6.8'
 sdk: org.kde.Sdk
 sdk-extensions:
   - org.freedesktop.Sdk.Extension.openjdk17