pythongh-111089: Use PyUnicode_AsUTF8() in sqlite3 (python#111122)

PyUnicode_AsUTF8() now raises an exception if the string contains
embedded null characters.

Modules/_sqlite/connection.c

@@ -76,15 +76,10 @@ isolation_level_converter(PyObject *str_or_none, const char **result)
         *result = NULL;
     }
     else if (PyUnicode_Check(str_or_none)) {
-        Py_ssize_t sz;
-        const char *str = PyUnicode_AsUTF8AndSize(str_or_none, &sz);
+        const char *str = PyUnicode_AsUTF8(str_or_none);
         if (str == NULL) {
             return 0;
         }
-        if (strlen(str) != (size_t)sz) {
-            PyErr_SetString(PyExc_ValueError, "embedded null character");
-            return 0;
-        }
 
         const char *level = get_isolation_level(str);
         if (level == NULL) {