Sertop has missing libraries

I ran sertop normally and I got this error. It was working before.
```
sertop: internal error, uncaught exception:
        Synterp.UnmappedLibrary(0, _)
```
sertop version:
```
8.19.0+0.19.2
```
coq-version:
```
The Coq Proof Assistant, version 8.20.0
compiled with OCaml 5.2.0
```
$COQLIB
```

```
(what's the default path for COQLIB?)