Fix directory targets with empty subdirs (#11226) #29954

Job	Run time
Documentation	3m 1s
Build (macos-latest, 5.1.x)	51s
Build (ubuntu-latest, 5.1.x)	8m 23s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 26s
Format	1m 7s
Build (4.14.x, ubuntu-latest, true)	2m 2s
Build (4.14.x, macos-latest, true)	53s
Build (5.1.x, macos-13, true)	4m 38s
Nix (macos-latest)	2m 6s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	8m 2s
Nix (ubuntu-latest)	51s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	7m 35s
Build (4.08.x, ubuntu-latest, true)	2m 19s
Build microbenchmarks	2m 32s
Coq 8.16.1	7m 6s
Create local opam switch (macos-latest, 5)	1m 54s
Build monorepo benchmark docker image	4m 8s
Wasm_of_ocaml	10m 24s
Create local opam switch (macos-latest, 4.14)	43s
Create local opam switch (ubuntu-latest, 5)	1m 53s
Create local opam switch (ubuntu-latest, 4.14)	1m 53s
	1h 13m 47s

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