Updating trunk VERSION from 6690.0 to 6691.0

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

Change-Id: Ia163fd0a1d147543923134ec9f98e31283caa17c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5828024
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1349574}