docs: Fix example to not produce validation errors

The previous approach generated the following error when a user has no emails

```
Processor BuiltinKindsEntityProcessor threw an error while validating the entity user:default/user; caused by TypeError: /spec/profile/email must NOT have fewer than 1 characters - limit: 1
```

Signed-off-by: Mike Bryant <mike.bryant@mettle.co.uk>

docs/integrations/github/org.md

@@ -189,8 +189,8 @@ returned identity.
 async (user, ctx): Promise<UserEntity | undefined> => {
   const entity = await defaultUserTransformer(user, ctx);
 
-  if (entity && user.organizationVerifiedDomainEmails) {
-    entity.spec.profile!.email = user.organizationVerifiedDomainEmails[0] || '';
+  if (entity && user.organizationVerifiedDomainEmails?.length) {
+    entity.spec.profile!.email = user.organizationVerifiedDomainEmails[0];
   }
 
   return entity;