Incrementing VERSION to 115.0.5790.18

Change-Id: Id53f56b64a789c802a5a5f57b4e66b6eede23a7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4587461
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/5790@{#335}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

chrome/VERSION

@@ -1,4 +1,4 @@
 MAJOR=115
 MINOR=0
 BUILD=5790
-PATCH=17
+PATCH=18