fix(merlin): tolerate files without extension #29069

Job	Run time
Build microbenchmarks	2m 31s
Coverage (5.1.x)	9m 28s
Build (macos-latest, 5.1.x)	13m 43s
Coq 8.16.1	7m 21s
Build (ubuntu-latest, 5.1.x)	8m 36s
Create local opam switch (macos-latest, 5)	5m 20s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	1m 40s
Documentation	56s
Format	1m 8s
Create local opam switch (macos-latest, 4.14)	5m 57s
Build (4.14.x, ubuntu-latest, true)	1m 24s
Create local opam switch (ubuntu-latest, 5)	4m 53s
Build (4.14.x, macos-latest, true)	2m 40s
Build monorepo benchmark docker image	4m 0s
Nix (macos-latest)	2m 20s
Create local opam switch (ubuntu-latest, 4.14)	4m 54s
Build (5.1.x, macos-13, true)	5m 53s
Nix (ubuntu-latest)	55s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	14m 35s
Wasm_of_ocaml	11m 6s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 17s
Build (4.08.x, ubuntu-latest, true)	1m 39s
Build (4.04.x, ubuntu-latest, true, true)	4m 46s
Build (4.02.x, ubuntu-latest, true)	4m 12s
	2h 8m 14s

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