Add `related_hetero_and_Proper` #609

Job	Run time
build (ubuntu-latest, 8.17.1, coq-8.17.1 libcoq-8.17.1-ocaml-dev, ppa:jgross-h/many-coq-versions-...	7m 56s
build (ubuntu-latest, 8.15.2, coq-8.15.2 libcoq-8.15.2-ocaml-dev, ppa:jgross-h/many-coq-versions-...	6m 52s
build (v8.15, coq libcoq-ocaml-dev, ppa:jgross-h/coq-8.15-daily, ubuntu-20.04)	7m 9s
check-all	1s
	21m 58s

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