Enable about credits generation

The whole about credit process validation has now been guarded behind a
flag in upstream code, which only gets enabled in official builds. This
has allowed broken PRs to get through master. This change enables the gn
value for all builds, so breakage can be detected as early as possible.

Chromium change:
https://chromium.googlesource.com/chromium/src/+/05db21cd6bc1decb3e90ca5eb152d7cea3bae19c

commit 05db21cd6bc1decb3e90ca5eb152d7cea3bae19c
Author: Fumitoshi Ukai <[email protected]>
Date:   Fri Aug 2 03:01:45 2024 +0000

    add gn arg `generate_about_credits`

    licenses.py is too slow on cog.
    allow disable about:credits generation.

    Bug: 355567690

build/commands/lib/config.js

@@ -426,6 +426,7 @@ Config.prototype.buildArgs = function () {
     brave_services_key_id: this.brave_services_key_id,
     service_key_aichat: this.service_key_aichat,
     service_key_stt: this.service_key_stt,
+    generate_about_credits: true,
   }
 
   if (!this.isBraveReleaseBuild()) {