ref: disable flaky test_count_transaction_with_valid_condition (#39295)

https://getsentry.atlassian.net/browse/TET-423

tests/sentry/snuba/metrics/test_metrics_layer/test_metrics_enhanced_performance.py

@@ -240,6 +240,7 @@ class PerformanceMetricsLayerTestCase(TestCase, BaseMetricsTestCase):
             key=lambda elem: elem["name"],
         )
 
+    @pytest.mark.skip(reason="flaky: TET-423")
     def test_count_transaction_with_valid_condition(self):
         for transaction, values in (
             ("<< unparameterized >>", [1]),