Rename the SECRETS_KEY page test to match what it actually checks

It only ever loaded the page and asserted the banner, never a password
save — but its name claimed the crash-on-save case, which is exactly the
promise that let that bug ship unnoticed once. The test that earns the
crash claim is its new neighbour, added for the same finding.

tests/Feature/Mail/MailSettingsPageTest.php

@@ -87,7 +87,7 @@ it('keeps the old password when the field is left empty', function () {
     expect($box->fresh()->password)->toBe('bleibt');
 });
 
-it('says so when SECRETS_KEY is missing, instead of crashing on the first password', function () {
+it('shows the SECRETS_KEY warning on the page', function () {
     config()->set('admin_access.secrets_key', '');
 
     Livewire::actingAs(User::factory()->operator('Owner')->create())