Fix Python 3.13 compat by adding missing attibute '_is_main_interpreter'

4383 · 4383 · commit 9a3775614ed0 · 2023-12-18T16:43:55.000+01:00
python/cpython#112826 Python 3.13 doesn't have workaround and so eventlet is broken with Python versions higher than 3.12. Fix eventlet#838 Fix eventlet#604
diff --git a/eventlet/green/thread.py b/eventlet/green/thread.py
@@ -15,6 +15,7 @@
 LockType = Lock
 __threadcount = 0
 
+_is_main_interpreter = __thread._is_main_interpreter
 
 if six.PY3:
     def _set_sentinel():
