Fix pam auth test regression (#33169) (#33174)

Backport #33169 by TheFox0x7

fixes: https://github.com/go-gitea/gitea/issues/33168

Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>

modules/auth/pam/pam_test.go

@@ -15,5 +15,5 @@ func TestPamAuth(t *testing.T) {
 	result, err := Auth("gitea", "user1", "false-pwd")
 	assert.Error(t, err)
 	assert.EqualError(t, err, "Authentication failure")
-	assert.Len(t, result)
+	assert.Empty(t, result)
 }