Updating trunk VERSION from 6403.0 to 6404.0

* This is an automated release commit.
* Do not revert without consulting chrome-pmo@google.com.
NOAUTOREVERT=true

Change-Id: Ie58862fb7c96ccab955c6b12e750fee2b59abf4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5432293
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1283587}