Add start_sha to UserCommitFilesRequestHeader

gitlab-ce#60609
4 jobs for webide-commit-use-correct-parent in 2 minutes and 2 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Test
passed #240463390
build

00:02:01

passed #240463391
check-grpc-proto-clients

00:01:23

passed #240463392
danger-review

00:01:07

passed #240463389
test

00:01:09