fix: guard Auth::guard('sanctum') call with try-catch in TeacherPortalAuthenticate

The TeacherPortalAuthenticate middleware called Auth::guard('sanctum')
without a try-catch, unlike MultiAuth and EnsurePrintRequestsAdminAccess
which already handle the InvalidArgumentException gracefully when the
sanctum guard driver is not yet registered.

This caused 'Auth guard [sanctum] is not defined' errors in tests when
the SanctumServiceProvider's driver registration hadn't completed before
middleware execution.

app/Http/Middleware/TeacherPortalAuthenticate.php

@@ -22,7 +22,11 @@ class TeacherPortalAuthenticate
             return $next($request);
         }
 
-        $sanctumUser = Auth::guard('sanctum')->user();
+        try {
+            $sanctumUser = Auth::guard('sanctum')->user();
+        } catch (\InvalidArgumentException) {
+            $sanctumUser = null;
+        }
         if ($sanctumUser) {
             Auth::setUser($sanctumUser);