Fix compilation with Coq 8.10 (which has a weaker `lia`).

4 jobs for ci/robbert/seq_S in 8 minutes and 29 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #109546
fp
build-coq.8.10.2

00:04:28

passed #109545
fp
build-coq.8.11.2

00:04:27

passed #109544
fp-timing
build-coq.8.12.1

00:04:03

passed #109543
fp
build-coq.dev

00:08:29