fix potential double-free in flisp table implementation (#53519)
In this case we would add two finalizers, leading to a double free.
Introduced by 5fc4ba91931526a08fc1bf8d3937aac731ee2cc6. However, I
believe we never hit this in the julia front end, since it requires
making a large pre-initialized table (i.e. with many arguments to
`table`) which is later freed. That tends not to happen since
initialized tables tend to be global constants.
