silence "From Coq" warning #2877

Job	Run time
opam-build (supported, ubuntu-latest)	4m 53s
opam-build (latest, ubuntu-latest)	4m 37s
nix	2m 5s
build (supported)	3m 28s
opam-build (dev, ubuntu-latest)	4m 23s
quick-build (supported, ubuntu-latest)	3m 10s
build (latest)	3m 14s
quick-build (latest, ubuntu-latest)	3m 8s
build (dev, --warnings)	3m 17s
quick-build (dev, ubuntu-latest)	3m 8s
doc-dep-graphs	7m 15s
doc-coqdoc	1m 27s
doc-alectryon	14m 51s
coqchk (supported)	1m 58s
coqchk (latest)	2m 3s
doc-timing	1m 46s
install (supported)	1m 38s
coqchk (dev)	1m 59s
install (latest)	1m 33s
install (dev)	1m 51s
deploy-doc	0s
delete-artifacts	7s
	1h 11m 51s

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