BraveMainSettingsFragmentTest.testPreferenceCount was failing on Release build. Reason: `kBraveRewards` feature is `FEATURE_DISABLED_BY_DEFAULT` on official builds, and this feature has effect on `PREF_BRAVE_VPN_CALLOUT`/`PREF_BRAVE_VPN` prefs. Excluded these prefs from calculation to get the same test result for official and non-official builds. Resolves https://github.com/brave/brave-browser/issues/53598