better error messages

1 job for ci/pldi21-submission-artifact in 12 minutes and 19 seconds (queued for 7 minutes and 28 seconds)
Name Stage Failure
build-coq.8.12.0 Build

## theories/lang/proofmode.v
13134948680;;instructions:u;3460477592;100.00;1.21;insn per cycle
real: 3.48, user: 3.17, sys: 0.30, mem: 566712 kB

[buildjob] Submitting timing information to coq-speed (Project: refinedc, Branch: ci/pldi21-submission-artifact, Config: build-coq.8.12.0)
curl: (22) The requested URL returned error: 500 Internal Server Error
ERROR: Job failed: exit code 1