Fix intermittent failures of test_circuitpadding_wronghop().

We fix it by disabling the scheduling of actual padding.
Fixes #29122.

changes/bug29122

@@ -0,0 +1,3 @@
+  o Minor bugfixes (unit tests):
+    - Fix intermittent failures on an adaptive padding unittest. Fixes bug
+      29122; bugfix on 0.4.0.1-alpha

src/test/test_circuitpadding.c

@@ -1239,6 +1239,10 @@ test_circuitpadding_wronghop(void *arg)
 
   MOCK(circuitmux_attach_circuit, circuitmux_attach_circuit_mock);
 
+  /* Mock this function so that our cell counting tests don't get confused by
+   * padding that gets sent by scheduled timers. */
+  MOCK(circpad_machine_schedule_padding,circpad_machine_schedule_padding_mock);
+
   client_side = (circuit_t *)origin_circuit_new();
   dummy_channel.cmux = circuitmux_alloc();
   relay_side = (circuit_t *)new_fake_orcirc(&dummy_channel,