Replace some `V`s with `i` and `j`s for consistency's sake.

3 jobs for gen_proofmode in 11 minutes and 39 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build-coq.8.7.1 #8901
fp

00:04:20

passed build-coq.8.7.2 #8900
fp-timing

00:03:25

passed build-coq.dev #8899
fp

00:11:39