Check field lengths instead of body size

This makes length limits more consistent.
5 jobs for master in 17 minutes and 1 second (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #360433147
build:webpack

00:02:29

 
  Test
passed #360433148
build:release

00:03:37

passed #360433152
test:1.39

00:04:14

passed #360433153
test:nightly

00:14:31

passed #360433149
test:stable

00:04:22