build(deps): bump bedrock2 from `6fcb247` to `cdf3a6f` #699

Job	Run time
build (master, coq libcoq-core-ocaml-dev, ppa:jgross-h/coq-master-daily)	4m 4s
build (8.18.0, coq-8.18.0 libcoq-8.18.0-ocaml-dev, ppa:jgross-h/many-coq-versions-ocaml-4-11)	3m 33s
coq-check-all	1s
	7m 38s

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