Fix invalid username popup being behind public game button (#951)

## Description:
one hour of fucking around with git later: fixes the invalid username
popup being behind the public game button and accepts the close label
fix from #949

![image](https://github.com/user-attachments/assets/ab65ab56-79fc-4c72-8c99-a50521c2faaf)

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

demonessica

src/client/UsernameInput.ts

@@ -47,7 +47,7 @@ export class UsernameInput extends LitElement {
       />
       ${this.validationError
         ? html`<div
-            class="absolute w-full mt-2 px-3 py-1 text-lg border rounded bg-white text-red-600 border-red-600 dark:bg-gray-700 dark:text-red-300 dark:border-red-300"
+            class="absolute z-10 w-full mt-2 px-3 py-1 text-lg border rounded bg-white text-red-600 border-red-600 dark:bg-gray-700 dark:text-red-300 dark:border-red-300"
           >
             ${this.validationError}
           </div>`