Updating trunk VERSION from 6387.0 to 6388.0

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

Change-Id: I6003fe349ffb47c65935aaf33e4615823c67adeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5405145
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1280167}