Issue #22117: Fix test_gdb for the new time.sleep()

Use time.gmtime() instead of time.sleep(), because time.sleep() is no more
declared with METH_VARARGS but with METH_O. time.gmtime() is still declared
with METH_VARARGS and so it is called with PyCFunction_Call() which is the
target of the test_gdb unit test.