pyportaltest: Allow registering a session close callback

This works around a race condition where test_close_session_signal
registers a callback but on slow systems the Close signal may be sent
before said callback can be registered.

Note that we need to keep the returned SessionResult alive so the
XdpSession isn't cleaned up by the Python GC before we finish the test.

Closes #166

tests/pyportaltest/test_remotedesktop.py

@@ -56,6 +56,7 @@ def create_session(
         start_session=True,
         persist_mode=None,
         restore_token=None,
+        cb_closed_signal=None,
     ) -> SessionSetup:
         params = params or {}
         # To make the tests easier, load ScreenCast automatically if we have
@@ -120,6 +121,9 @@ def create_session_done(portal, task, data):
 
         assert session.get_session_type() == Xdp.SessionType.REMOTE_DESKTOP
 
+        if cb_closed_signal:
+            session.connect("closed", cb_closed_signal)
+
         if outputs:
             # open the PW remote by default since we need it anyway for Start()
             handle = session.open_pipewire_remote()
@@ -581,9 +585,6 @@ def test_close_session_signal(self):
         Ensure that we get the GObject signal when our session is closed
         externally.
         """
-        params = {"close-after-start": 500}
-        setup = self.create_session(params=params)
-        session = setup.session
 
         session_closed_signal_received = False
 
@@ -592,8 +593,10 @@ def session_closed(session):
             session_closed_signal_received = True
             self.mainloop.quit()
 
-        session.connect("closed", session_closed)
-
+        params = {"close-after-start": 500}
+        _ = self.create_session(
+            params=params, cb_closed_signal=session_closed
+        )  # keep SessionResult alive
         self.mainloop.run()
 
         assert session_closed_signal_received is True