fix: updates username validation to allow for all special character u…

…sage (#9946)

### What?

Previously, only `.` & `-` special chars were allowed in usernames

### How?

Now - all special chars are accepted during username creating like `@`

packages/payload/src/fields/validations.ts

@@ -232,8 +232,8 @@ export const username: UsernameFieldValidation = (
     return t('validation:shorterThanMax', { maxLength })
   }
 
-  if ((value && !/^[\w.-]+$/.test(value)) || (!value && required)) {
-    return t('validation:username')
+  if (!value && required) {
+    return t('validation:required')
   }
 
   return true