build(deps): bump bedrock2 from `7603637` to `ab6f7a1` #630

Job	Run time
build (8.17.0, coq-8.17.0 libcoq-8.17.0-ocaml-dev, ppa:jgross-h/many-coq-versions-ocaml-4-11)	3m 42s
build (master, coq libcoq-core-ocaml-dev, ppa:jgross-h/coq-master-daily)	3m 40s
	7m 22s

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