Disable gdbus/gvfs usage when running tests
Disable gdbus/gvfs usage when running tests

The gvfsdbus backend adds a lot of runtime state and activity
highly dependent on local configuration. Even if it may reveal
problems in our event loop code, the added noise and lack of
predictability is unwelcome for testing and the debug tools.

gi-rust/gobject-sys,gi-rust/gio-sys,gi-rust/grust,gi-rust/grust-proof,gi-rust/glib-sys