benchmark: rename startup.js to startup-core.js

It is easier to filter the core startup benchmark with this name.

PR-URL: #51669
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

.github/CODEOWNERS

@@ -125,7 +125,7 @@
 
 # Startup
 
-/benchmark/misc/startup.js @nodejs/startup
+/benchmark/misc/startup-* @nodejs/startup
 /lib/internal/bootstrap/* @nodejs/startup
 /src/node_builtins* @nodejs/startup
 /src/node_realm* @nodejs/startup @nodejs/realm