OCaml 5.5 support

#=== ERROR while compiling ocamlmerlin-mlx.0.11 ===============================#
# context              2.6.0~alpha1~dev | linux/x86_64 | ocaml-variants.5.5.0+trunk | file:///home/opam/opam-repository
# path                 ~/.opam/5.5/.opam-switch/build/ocamlmerlin-mlx.0.11
# command              ~/.opam/5.5/bin/dune build -p ocamlmerlin-mlx -j 1 @install
# exit-code            1
# env-file             ~/.opam/log/ocamlmerlin-mlx-14-8a8200.env
# output-file          ~/.opam/log/ocamlmerlin-mlx-14-8a8200.out
### output ###
# (cd _build/default && /home/opam/.opam/5.5/bin/ocamlc.opt -open=Mlx_ocaml_utils -open=Mlx_ocaml_parsing -open=Mlx_ocaml_compression -open=Mlx_utils -w -40 -w -9 -g -bin-annot -bin-annot-occurrences -I ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/byte -I /home/opam/.opam/5.5/lib/merlin-lib/config -I /home/opam/.opam/5.5/lib/ocaml-compiler-libs/common -I /home/opam/.opam/5.5/lib/ocaml-compiler-libs/shadow -I /home/opam/.opam/5.5/lib/ocaml/compiler-libs -I /home/opam/.opam/5.5/lib/ocaml/str -I /home/opam/.opam/5.5/lib/ocaml/unix -I /home/opam/.opam/5.5/lib/ppx_derivers -I /home/opam/.opam/5.5/lib/ppxlib -I /home/opam/.opam/5.5/lib/ppxlib/ast -I /home/opam/.opam/5.5/lib/ppxlib/astlib -I /home/opam/.opam/5.5/lib/ppxlib/print_diff -I /home/opam/.opam/5.5/lib/ppxlib/stdppx -I /home/opam/.opam/5.5/lib/ppxlib/traverse_builtins -I /home/opam/.opam/5.5/lib/sexplib0 -I /home/opam/.opam/5.5/lib/stdlib-shims -I ocamlmerlin_mlx/ocaml/compression/.mlx_ocaml_compression.objs/byte -I ocamlmerlin_mlx/ocaml/parsing/.mlx_ocaml_parsing.objs/byte -I ocamlmerlin_mlx/ocaml/utils/.mlx_ocaml_utils.objs/byte -I ocamlmerlin_mlx/utils/.mlx_utils.objs/byte -cmi-file ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/byte/mlx_ocaml_typing__Short_paths.cmi -no-alias-deps -open Mlx_ocaml_typing -o ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/byte/mlx_ocaml_typing__Short_paths.cmo -c -impl ocamlmerlin_mlx/ocaml/typing/short_paths.ml)
# File "ocamlmerlin_mlx/ocaml/typing/short_paths.ml", lines 1128-1131, characters 4-43:
# 1128 | ....let Basis { history } = t.kind in
# 1129 |     History.commit history rev_deps diff;
# 1130 |     t.graph <- graph;
# 1131 |     Todo.mutate graph rev_deps t.todos diff
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
#   Here is an example of a case that is not matched:
#     Env {parent={kind=Basis _; todos={ _ }; _ }; _ }
# (cd _build/default && /home/opam/.opam/5.5/bin/ocamlopt.opt -open=Mlx_ocaml_utils -open=Mlx_ocaml_parsing -open=Mlx_ocaml_compression -open=Mlx_utils -w -40 -w -9 -g -I ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/byte -I ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/native -I /home/opam/.opam/5.5/lib/merlin-lib/config -I /home/opam/.opam/5.5/lib/ocaml-compiler-libs/common -I /home/opam/.opam/5.5/lib/ocaml-compiler-libs/shadow -I /home/opam/.opam/5.5/lib/ocaml/compiler-libs -I /home/opam/.opam/5.5/lib/ocaml/str -I /home/opam/.opam/5.5/lib/ocaml/unix -I /home/opam/.opam/5.5/lib/ppx_derivers -I /home/opam/.opam/5.5/lib/ppxlib -I /home/opam/.opam/5.5/lib/ppxlib/ast -I /home/opam/.opam/5.5/lib/ppxlib/astlib -I /home/opam/.opam/5.5/lib/ppxlib/print_diff -I /home/opam/.opam/5.5/lib/ppxlib/stdppx -I /home/opam/.opam/5.5/lib/ppxlib/traverse_builtins -I /home/opam/.opam/5.5/lib/sexplib0 -I /home/opam/.opam/5.5/lib/stdlib-shims -I ocamlmerlin_mlx/ocaml/compression/.mlx_ocaml_compression.objs/byte -I ocamlmerlin_mlx/ocaml/compression/.mlx_ocaml_compression.objs/native -I ocamlmerlin_mlx/ocaml/parsing/.mlx_ocaml_parsing.objs/byte -I ocamlmerlin_mlx/ocaml/parsing/.mlx_ocaml_parsing.objs/native -I ocamlmerlin_mlx/ocaml/utils/.mlx_ocaml_utils.objs/byte -I ocamlmerlin_mlx/ocaml/utils/.mlx_ocaml_utils.objs/native -I ocamlmerlin_mlx/utils/.mlx_utils.objs/byte -I ocamlmerlin_mlx/utils/.mlx_utils.objs/native -cmi-file ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/byte/mlx_ocaml_typing__Short_paths.cmi -no-alias-deps -open Mlx_ocaml_typing -o ocamlmerlin_mlx/ocaml/typing/.mlx_ocaml_typing.objs/native/mlx_ocaml_typing__Short_paths.cmx -c -impl ocamlmerlin_mlx/ocaml/typing/short_paths.ml)
# File "ocamlmerlin_mlx/ocaml/typing/short_paths.ml", lines 1128-1131, characters 4-43:
# 1128 | ....let Basis { history } = t.kind in
# 1129 |     History.commit history rev_deps diff;
# 1130 |     t.graph <- graph;
# 1131 |     Todo.mutate graph rev_deps t.todos diff
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
#   Here is an example of a case that is not matched:
#     Env {parent={kind=Basis _; todos={ _ }; _ }; _ }

Start with ocamlmerlin_mlx/ocaml/typing/short_paths.ml around lines 1128-1131 and inspect the surrounding handling of t.kind. Reproduce the failure with dune build -p ocamlmerlin-mlx -j 1 @install under OCaml 5.5. Done means ocamlmerlin-mlx builds successfully without warning 8 being treated as an error.