also declare compatibility with Coq 8.9 in opam file

28 jobs for master in 27 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #19514
fp
build-coq.8.6.0

00:03:02

passed #19513
fp
build-coq.8.6.1

00:02:56

passed #19512
fp
build-coq.8.7.0

00:02:56

passed #19051
fp
build-coq.8.7.1

00:08:29

passed #18974
fp-timing
build-coq.8.7.2

00:07:56

passed #18973
fp-timing
build-coq.8.8.0

00:02:21

passed #19052
fp
build-coq.8.8.1

00:02:20

passed #18971
fp
build-coq.8.8.2

00:02:14

canceled #19515
fp
build-coq.8.9.dev

00:05:27

canceled #19516
fp
build-coq.dev

00:01:08

passed #18978
fp
build-coq.8.6.0

00:08:11

passed #19043
fp
build-coq.8.6.0

00:02:27

passed #19049
fp
build-coq.8.6.0

00:08:32

passed #18977
fp
build-coq.8.6.1

00:08:08

passed #19050
fp
build-coq.8.6.1

00:02:14

passed #19044
fp
build-coq.8.6.1

00:02:30

passed #18976
fp
build-coq.8.7.0

00:08:06

passed #19055
fp
build-coq.8.7.0

00:08:10

passed #19048
fp
build-coq.8.7.1

00:02:16

passed #18975
fp
build-coq.8.7.1

00:08:17

passed #19045
fp
build-coq.8.8.1

00:02:34

passed #18972
fp
build-coq.8.8.1

00:08:19

passed #18970
fp
build-coq.8.9.dev

00:09:03

passed #19053
fp
build-coq.8.9.dev

00:03:02

passed #19046
fp
build-coq.8.9.dev

00:06:38

passed #18969
fp
build-coq.dev

00:20:04

passed #19047
fp
build-coq.dev

00:20:00

passed #19054
fp
build-coq.dev

00:20:11