properly pin ssreflect

3 jobs for master in 16 minutes and 57 seconds (queued for 11 minutes and 32 seconds)
Status Job ID Name Coverage
  Build
passed #23209
fp
build-coq.8.6.1

00:12:29

passed #23208
fp
build-coq.8.7.2

00:02:08

passed #23207
fp
build-coq.8.8.2

00:02:19