fix dune-project version #3948

Job	Run time
opam-build (dev, ubuntu-latest)	4m 12s
nix	2m 14s
opam-build (9.1, ubuntu-latest)	2m 0s
opam-build (9.0, ubuntu-latest)	2m 3s
build (9.0)	3m 20s
build (dev, --warnings)	3m 47s
quick-build (9.1, ubuntu-latest)	3m 12s
quick-build (9.0, ubuntu-latest)	3m 9s
quick-build (dev, ubuntu-latest)	3m 15s
build (9.1)	3m 22s
doc-dep-graphs	7m 37s
doc-coqdoc	1m 36s
doc-alectryon	12m 5s
install (9.0)	1m 44s
doc-timing	1m 34s
coqchk (9.1)	1m 54s
coqchk (dev)	1m 56s
install (dev)	1m 43s
coqchk (9.0)	1m 46s
install (9.1)	1m 49s
delete-artifacts	6s
deploy-doc	0s
	1h 4m 24s

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