change when we perform GC run in test_webview

This makes it clear that we don't collect the WebView from the current test run (which is still referenced by fixtures) but from the previous run.

testbed/tests/widgets/test_webview.py

@@ -79,6 +79,13 @@ async def on_load():
 
 @pytest.fixture
 async def widget(on_load):
+    if toga.platform.current_platform == "linux":
+        # On Gtk, ensure that the WebView from a previous test run is garbage collected.
+        # This prevents a segfault at GC time likely coming from the test suite running
+        # in a thread and Gtk WebViews sharing resources between instances. We perform
+        # the GC run here since pytest fixtures make earlier cleanup difficult.
+        gc.collect()
+
     widget = toga.WebView(style=Pack(flex=1), on_webview_load=on_load)
     # We shouldn't be able to get a callback until at least one tick of the event loop
     # has completed.
@@ -104,14 +111,7 @@ async def widget(on_load):
             else:
                 raise
 
-    yield widget
-
-    if toga.platform.current_platform == "linux":
-        # On Gtk, ensure that the WebView is garbage collection before the next test
-        # case. This prevents a segfault at GC time likely coming from the test suite
-        # running in a thread and Gtk WebViews sharing resources between instances.
-        del widget
-        gc.collect()
+    return widget
 
 
 async def test_set_url(widget, probe, on_load):