run: Use a constant path for the reference to per-app directories
run: Use a constant path for the reference to per-app directories

It's a bit simpler to get a per-app XDG_RUNTIME_DIR safely if we avoid
putting this in there. Nothing relies on it being in the
XDG_RUNTIME_DIR.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak