test proofmode output for long lines, and fix it

4 jobs for gen_proofmode in 27 minutes and 12 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #13360
fp
build-coq.8.7.1

00:04:42

passed #13359
fp-timing
build-coq.8.7.2

00:04:25

passed #13358
fp-timing
build-coq.8.8.0

00:04:23

passed #13357
fp
build-coq.dev

00:27:11