test: fix flaky timing in test_cancel_terminated_invocation (#619)

Replace the fixed 150ms sleep with a deadline-bounded poll loop. On
slower CI runners (e.g., Python 3.11 on GitHub Actions) the executor
had not yet posted done.invoke.loading when the assertion ran, leaving
the configuration in 'loading' instead of 'ready'.

The new loop drives the processing loop in 20ms ticks until the final
state is reached, with a 2s ceiling.

Signed-off-by: Fernando Macedo <fgmacedo@gmail.com>

Author: fgmacedo

tests/test_invoke.py

@@ -614,8 +614,10 @@ class SM(StateChart):
             done_invoke_loading = loading.to(ready)
 
         sm = await sm_runner.start(SM)
-        await sm_runner.sleep(0.15)
-        await sm_runner.processing_loop(sm)
+        deadline = time.monotonic() + 2.0
+        while "ready" not in sm.configuration_values and time.monotonic() < deadline:
+            await sm_runner.sleep(0.02)
+            await sm_runner.processing_loop(sm)
 
         assert "ready" in sm.configuration_values
         # All invocations should be terminated by now