bug#54094: frama-c doesn't start

[raingloom]

I was just idly messing around so I'm not super motivated to dig
deeper.

```
guix shell frama-c -- frama-c
[kernel] User Error: [findlib] package 'ocamlgraph' not found (required by 
`frama-c.kernel')
[kernel] User Error: Deferred error message was emitted during execution. See 
above messages for more information.
[kernel] Frama-C aborted: invalid user input.
```