example data: Change realmIcon default value in eg.serverSettings

Observed value for CZO is:

  /user_avatars/2/realm/icon.png?version=3

A relative URL rather than absolute, so change it to match that
observed value. API docs do not specify a format, see:
  #1860 (comment)

Also `GetServerSettingsResult.realmIcon` was never read before so
it's NFC change in regards to the tests.

Author: rajveermalviya

test/example_data.dart

@@ -92,6 +92,9 @@ int utcTimestamp([DateTime? dateTime]) {
 final Uri realmUrl = Uri.parse('https://chat.example/');
 Uri get _realmUrl => realmUrl;
 
+final Uri realmIcon = Uri.parse('/user_avatars/2/realm/icon.png?version=3');
+Uri get _realmIcon => realmIcon;
+
 const String recentZulipVersion = '9.0';
 const int recentZulipFeatureLevel = 382;
 const int futureZulipFeatureLevel = 9999;
@@ -125,7 +128,7 @@ GetServerSettingsResult serverSettings({
     requireEmailFormatUsernames: requireEmailFormatUsernames ?? true,
     realmUrl: realmUrl ?? _realmUrl,
     realmName: realmName ?? 'Example Zulip organization',
-    realmIcon: realmIcon ?? Uri.parse('$realmUrl/icon.png'),
+    realmIcon: realmIcon ?? _realmIcon,
     realmDescription: realmDescription ?? 'An example Zulip organization',
     realmWebPublicAccessEnabled: realmWebPublicAccessEnabled ?? false,
   );