fix(pkg): print depexts message when a program is not found #28648

Job	Run time
Build microbenchmarks	2m 18s
Coverage (5.1.x)	4m 11s
Coq 8.16.1	4m 11s
Build (macos-latest, 5.1.x)	3m 59s
Build (ubuntu-latest, 5.1.x)	4m 11s
Create local opam switch (macos-latest, 5)	4m 11s
Documentation	50s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	4m 10s
Create local opam switch (macos-latest, 4.14)	4m 15s
Format	1m 2s
Build (4.14.x, ubuntu-latest, true)	1m 30s
Create local opam switch (ubuntu-latest, 5)	4m 10s
Build (4.14.x, macos-latest, true)	4m 0s
Build monorepo benchmark docker image	3m 51s
Create local opam switch (ubuntu-latest, 4.14)	4m 11s
Build (5.1.x, macos-13, true)	4m 11s
Nix (macos-latest)	1s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	3m 58s
Nix (ubuntu-latest)	52s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	3m 57s
Build (4.08.x, ubuntu-latest, true)	1m 42s
Build (4.04.x, ubuntu-latest, true, true)	4m 2s
Build (4.02.x, ubuntu-latest, true)	4m 6s
	1h 13m 49s

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