Hardcode ott-username input name in DefaultLoginPageGeneratingFilter

- GenerateOneTimeTokenFilter uses `"username"`, the default UI should use the same parameter name

web/src/test/java/org/springframework/security/web/authentication/DefaultLoginPageGeneratingFilterTests.java

@@ -199,7 +199,7 @@ public class DefaultLoginPageGeneratingFilterTests {
 				        <h2>Request a One-Time Token</h2>
 				<p>
 				          <label for="ott-username" class="screenreader">Username</label>
-				          <input type="text" id="ott-username" name="null" placeholder="Username" required>
+				          <input type="text" id="ott-username" name="username" placeholder="Username" required>
 				        </p>
 				          <button class="primary" type="submit" form="ott-form">Send Token</button>
 				      </form>