{tool,client}: bump node version (#12840)

Bump node version to latest lts on the 18.x line which is 18.20.4 at the time of writing.

Updates https://github.com/tailscale/corp/issues/21741

Signed-off-by: Mario Minardi <mario@tailscale.com>

client/web/package.json

@@ -3,7 +3,7 @@
   "version": "0.0.1",
   "license": "BSD-3-Clause",
   "engines": {
-    "node": "18.16.1",
+    "node": "18.20.4",
     "yarn": "1.22.19"
   },
   "type": "module",

tool/node.rev

@@ -1 +1 @@
-18.16.1
+18.20.4