chore: Update matrix ID localization

lib/l10n/intl_en.arb

@@ -3498,5 +3498,6 @@
   "appIntro": "With FluffyChat you can chat with your friends. It's a secure decentralized [matrix] messenger! Learn more on https://matrix.org if you like or just sign up.",
   "theProcessWasCanceled": "The process was canceled.",
   "join": "Join",
-  "searchOrEnterHomeserverAddress": "Search or enter homeserver address"
+  "searchOrEnterHomeserverAddress": "Search or enter homeserver address",
+  "matrixId": "Matrix ID"
 }

lib/pages/login/login_view.dart

@@ -56,7 +56,7 @@ class LoginView extends StatelessWidget {
                       errorText: controller.usernameError,
                       errorStyle: const TextStyle(color: Colors.orange),
                       hintText: '@username:domain',
-                      labelText: L10n.of(context).emailOrUsername,
+                      labelText: L10n.of(context).matrixId,
                     ),
                   ),
                 ),