Incrementing VERSION to 129.0.6668.48

Change-Id: I8d4b220af902e7a277ffd6273691f9282bffa9d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5850215
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/6668@{#1155}
Cr-Branched-From: 05bc6649-refs/heads/main@{#1343869}