test-flatpak-demo: Rename to remove from the SDK-only tests

The corresponding LAVA test is moving away from being SDK-only, so move the file here to match.

https://phabricator.apertis.org/T8170

IMPORTANT NOTE: This should be merged in tandem with tests/apertis-test-cases!356 (merged)

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