Updating trunk VERSION from 4817.0 to 4818.0

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

Change-Id: If5f4d3ac3100010681ff97a1bbf0ef8dd337d639
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3375683
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#956901}