gh-134411: assert PyLong_FromLong(x) != NULL when x is known to be small (#134415)

Since `PyLong_From Long(PY_MONITORING_DEBUGGER_ID)` falls to `small_int` case and can't return `NULL`. Added `assert`s for extra confidence.
#134411 (comment)

Author: smurav

Python/instrumentation.c

@@ -2558,18 +2558,22 @@ PyObject *_Py_CreateMonitoringObject(void)
     err = PyObject_SetAttrString(events, "NO_EVENTS", _PyLong_GetZero());
     if (err) goto error;
     PyObject *val = PyLong_FromLong(PY_MONITORING_DEBUGGER_ID);
+    assert(val != NULL); /* Can't return NULL because the int is small. */
     err = PyObject_SetAttrString(mod, "DEBUGGER_ID", val);
     Py_DECREF(val);
     if (err) goto error;
     val = PyLong_FromLong(PY_MONITORING_COVERAGE_ID);
+    assert(val != NULL);
     err = PyObject_SetAttrString(mod, "COVERAGE_ID", val);
     Py_DECREF(val);
     if (err) goto error;
     val = PyLong_FromLong(PY_MONITORING_PROFILER_ID);
+    assert(val != NULL);
     err = PyObject_SetAttrString(mod, "PROFILER_ID", val);
     Py_DECREF(val);
     if (err) goto error;
     val = PyLong_FromLong(PY_MONITORING_OPTIMIZER_ID);
+    assert(val != NULL);
     err = PyObject_SetAttrString(mod, "OPTIMIZER_ID", val);
     Py_DECREF(val);
     if (err) goto error;