gh-153568: Skip GC pause without the GIL

Author: pablogsal

Parser/asdl_c.py

@@ -2116,15 +2116,20 @@ class PartingShots(StaticVisitor):
     if (state == NULL) {
         return NULL;
     }
+#ifndef Py_GIL_DISABLED
     // Freshly converted AST nodes cannot be part of a reference cycle yet,
     // so a garbage collection while building them cannot free anything of
     // this tree and only pays to traverse its half-built nodes. Pause the
-    // collector while the conversion runs.
+    // collector while the conversion runs. PyGC_Disable() is interpreter-wide,
+    // so this optimization is not safe in a free-threaded build.
     int gc_was_enabled = PyGC_Disable();
+#endif
     PyObject *result = ast2obj_mod(state, t);
+#ifndef Py_GIL_DISABLED
     if (gc_was_enabled) {
         PyGC_Enable();
     }
+#endif
 
     return result;
 }