Fix compilation with master #299

Job	Run time
build (mathcomp/mathcomp:2.0.0-coq-8.16)	17m 37s
build (mathcomp/mathcomp:2.0.0-coq-8.17)	22m 15s
build (mathcomp/mathcomp:2.0.0-coq-8.18)	15m 14s
build (mathcomp/mathcomp:2.0.0-coq-8.16)	32m 9s
build (mathcomp/mathcomp:2.1.0-coq-8.17)	11m 26s
build (mathcomp/mathcomp:2.1.0-coq-8.18)	5m 44s
build (mathcomp/mathcomp:2.1.0-coq-dev)	4m 5s
build (mathcomp/mathcomp-dev:coq-8.16)	38m 12s
build (mathcomp/mathcomp-dev:coq-8.17)	44m 29s
build (mathcomp/mathcomp-dev:coq-8.18)	40m 15s
build (mathcomp/mathcomp-dev:coq-dev)	4m 11s
	3h 55m 37s

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