0.17 doesn't compile with OCaml 5.5

And on check.ocaml.ci [too](https://check.ci.ocaml.org/?comp=4.11&comp=4.14&comp=5.2&comp=5.4&comp=5.5&available=4.11&available=4.14&available=5.2&available=5.4&available=5.5&show-only=good&show-only=partial&show-only=bad&show-only=not-available&show-only=internal-failure&packages=accessor_core&maintainers=&logsearch=&logsearch_comp=4.11)

```
# path /mnt/work/.opam/5.5.0+flambda/.opam-switch/build/accessor_core.v0.17.0
# command /mnt/work/.opam/5.5.0+flambda/bin/dune build -p accessor_core -j 5
# exit-code 1
# env-file /mnt/work/.opam/log/accessor_core-9882-44f850.env
# output-file /mnt/work/.opam/log/accessor_core-9882-44f850.out
### output ###
# (cd _build/default && /mnt/work/.opam/5.5.0+flambda/bin/ocamlc.opt -w -40 -g -bin-annot -bin-annot-occurrences -I src/.accessor_core.objs/byte -I /mnt/work/.opam/5.5.0+flambda/lib/accessor -I /mnt/work/.opam/5.5.0+flambda/lib/accessor/applicative_without_return -I /mnt/work/.opam/5.5.0+flambda/lib/accessor_base -I /mnt/work/.opam/5.5.0+flambda/lib/base -I /mnt/work/.opam/5.5.0+flambda/lib/bas[...]
# File "src/accessor_gc.mli", line 52, characters 5-24:
# 52 | with type t := Gc.Stat.t
# ^^^^^^^^^^^^^^^^^^^
# Error: This variant or record definition does not match that of type
# Core.Gc.Stat.t
# An extra field, live_stacks_words, is provided in the original definition.
```

Start by reproducing the failure with `dune build -p accessor_core` under OCaml 5.5, then inspect `src/accessor_gc.mli` around line 52 and the reported `Core.Gc.Stat.t` mismatch. Done means accessor_core compiles successfully on OCaml 5.5 and the corresponding check.ocaml.ci result no longer fails.

Written by the indexing model from the issue text.