gh-115482: Assume the Main Interpreter is Always Running "main" (gh-115484)

gh-115482: Assume the Main Interpreter is Always Running "main" (gh-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.