gh-103092: Make _elementtree module importable in sub-interpreters (#113434)

Enable imports of _elementtree module in sub-interpreters

Author: Eclips4

Modules/_elementtree.c

@@ -4430,9 +4430,7 @@ module_exec(PyObject *m)
 
 static struct PyModuleDef_Slot elementtree_slots[] = {
     {Py_mod_exec, module_exec},
-    // XXX gh-103092: fix isolation.
-    {Py_mod_multiple_interpreters, Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED},
-    //{Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
+    {Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
     {0, NULL},
 };