Free arena on _PyCompile_AstOptimize failure in Py_CompileStringObject (GH-127910)

After commit 10a91d7e9 introduced arena cleanup, commit 2dfbd4f36
removed the free call when _PyCompile_AstOptimize fails.

Python/pythonrun.c

@@ -1486,6 +1486,7 @@ Py_CompileStringObject(const char *str, PyObject *filename, int start,
     if (flags && (flags->cf_flags & PyCF_ONLY_AST)) {
         if ((flags->cf_flags & PyCF_OPTIMIZED_AST) == PyCF_OPTIMIZED_AST) {
             if (_PyCompile_AstOptimize(mod, filename, flags, optimize, arena) < 0) {
+                _PyArena_Free(arena);
                 return NULL;
             }
         }