switch to Int in cring_Z #2505

Job	Run time
quick-build (supported, ubuntu-latest)	2m 42s
quick-build (latest, ubuntu-latest)	2m 45s
nix	2m 8s
opam-build (supported, ubuntu-latest)	4m 35s
quick-build (dev, ubuntu-latest)	2m 41s
build (supported)	3m 2s
opam-build (latest, ubuntu-latest)	4m 30s
build (latest)	3m 1s
opam-build (dev, ubuntu-latest)	4m 22s
build (dev, --warnings)	3m 43s
doc-coqdoc	1m 5s
doc-dep-graphs	7m 37s
coqchk (supported)	1m 30s
doc-alectryon	15m 10s
coqchk (latest)	1m 30s
coqchk (dev)	1m 20s
doc-timing	1m 3s
install (supported)	1m 14s
install (latest)	1m 25s
install (dev)	1m 4s
deploy-doc	0s
delete-artifacts	5s
	1h 6m 32s

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