Fix incorrect Flatpak branch

https://phabricator.apertis.org/T8363



Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

test-cases/hmi-video-load.yaml

@@ -22,7 +22,7 @@ run:
    - "Add the Apertis Flatpak repository (only needed on SDK images)"
    - $ flatpak remote-add --user --if-not-exists apertis https://images.apertis.org/flatpak/repo/apertis.flatpakrepo
    - "Install Totem (only needed on SDK images)"
-   - $ flatpak install --user apertis org.apertis.hmi.totem//${APERTIS_RELEASE}
+   - $ flatpak install --user apertis org.apertis.hmi.totem//stable
    - "On the agl-compositor click on the menu icon"
    - "Observe that the Videos app icon is visible"
    - "Launch Videos app"

test-cases/hmi-video-play-pause.yaml

@@ -22,7 +22,7 @@ run:
    - "Add the Apertis Flatpak repository (only needed on SDK images)"
    - $ flatpak remote-add --user --if-not-exists apertis https://images.apertis.org/flatpak/repo/apertis.flatpakrepo
    - "Install Totem (only needed on SDK images)"
-   - $ flatpak install --user apertis org.apertis.hmi.totem//${APERTIS_RELEASE}
+   - $ flatpak install --user apertis org.apertis.hmi.totem//stable
    - "On the agl-compositor click on the menu icon"
    - "Observe that the Videos app icon is visible"
    - "Launch Videos app"