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.

Closes #166

tests/pyportaltest/test_remotedesktop.py

@@ -55,6 +55,7 @@ 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
@@ -119,6 +120,9 @@ 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()
@@ -580,9 +584,6 @@ 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
 
@@ -591,8 +592,8 @@ 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)
         self.setup_mainloop_with_timeout(timeout_ms=0).run()
 
         assert session_closed_signal_received is True