Issue #23694: Enhance _Py_fopen(), it now raises an exception on error

* If fopen() fails, OSError is raised with the original filename object.
* The GIL is now released while calling fopen()

Python/import.c

@@ -1945,8 +1945,6 @@ _imp_load_dynamic_impl(PyModuleDef *module, PyObject *name, PyObject *path, PyOb
         fp = _Py_fopen_obj(path, "r");
         if (fp == NULL) {
             Py_DECREF(path);
-            if (!PyErr_Occurred())
-                PyErr_SetFromErrno(PyExc_IOError);
             return NULL;
         }
     }