adapting docker images to mathcomp 2.4 (#42) #84

Job	Run time
build (mathcomp/mathcomp:2.2.0-coq-8.19)	6m 22s
build (mathcomp/mathcomp:2.3.0-coq-8.20)	6m 22s
build (mathcomp/mathcomp:2.4.0-rocq-prover-9.0)	4m 28s
build (mathcomp/mathcomp-dev:rocq-prover-dev)	13m 41s
	30m 53s

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