pythongh-115482: Assume the Main Interpreter is Always Running "main" (…

…pythongh-115484)

This is a temporary fix to unblock embedders that do not call Py_Main().

_PyInterpreterState_IsRunningMain() will always return true for the main interpreter, even in corner cases where it technically should not. The (future) full solution will do the right thing in those corner cases.

Python/pystate.c

@@ -1044,7 +1044,14 @@ _PyInterpreterState_SetNotRunningMain(PyInterpreterState *interp)
 int
 _PyInterpreterState_IsRunningMain(PyInterpreterState *interp)
 {
-    return (interp->threads.main != NULL);
+    if (interp->threads.main != NULL) {
+        return 1;
+    }
+    // For now, we assume the main interpreter is always running.
+    if (_Py_IsMainInterpreter(interp)) {
+        return 1;
+    }
+    return 0;
 }
 
 int