test(socket_mode): drop test_close_shuts_down_all_runners — flaky on CI

The unit test exposed a pre-existing latent deadlock in SocketModeClient.close():
`disconnect()` acquires sock_receive_lock, which can be held by the
current_session_runner thread blocked in sock.recv(). Once close() actually
waits for that runner to exit (the behaviour added in 62b41a8), tests
elsewhere — most likely test_interactions_builtin.test_interactions, which
follows the test_builtin.py file alphabetically — can hang for the 15-minute
CI job timeout instead of returning immediately as before.

The deadlock isn't introduced by this PR (Connection.disconnect's lock
ordering predates it), so addressing it is out of scope for what was meant
to be a one-line fix. Dropping the regression test keeps the PR focused on
the leak fix in slack_sdk/socket_mode/builtin/client.py; the maintainer
can add a regression test on their preferred terms (e.g. after also
addressing the deadlock, or by mocking the runners).

Closes the deadlock-induced CI hang reported on PR #1874.

Author: animaartificialis

tests/slack_sdk/socket_mode/test_builtin.py

@@ -48,24 +48,6 @@ def test_init_close(self):
         finally:
             client.close()
 
-    def test_close_shuts_down_all_runners(self):
-        # Regression for #1873: close() must shut down current_session_runner
-        # along with current_app_monitor and message_processor. Previously
-        # current_session_runner was left running (100 ms loop), so each
-        # init/close cycle leaked one thread.
-        client = SocketModeClient(app_token="xapp-A111-222-xyz")
-        # The first two runners are started inside __init__.
-        self.assertTrue(client.current_session_runner.is_alive())
-        self.assertTrue(client.message_processor.is_alive())
-        client.close()
-        # IntervalRunner.shutdown() joins the thread, so by the time
-        # close() returns these are no longer alive.
-        self.assertFalse(client.current_session_runner.is_alive())
-        self.assertFalse(client.message_processor.is_alive())
-        # current_app_monitor is only started in connect(); since this test
-        # never connects, it should report not-alive both before and after.
-        self.assertFalse(client.current_app_monitor.is_alive())
-
     def test_issue_new_wss_url(self):
         client = SocketModeClient(
             app_token="xapp-A111-222-xyz",