Incrementing VERSION to 91.0.4468.4

Change-Id: Ia282deac13219b7e9f4a243bd7c7a3788c091984
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2808993
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/4468@{#7}
Cr-Branched-From: 6ff41c3-refs/heads/master@{#869340}

chrome/VERSION

@@ -1,4 +1,4 @@
 MAJOR=91
 MINOR=0
 BUILD=4468
-PATCH=3
+PATCH=4