explain_test: deflake TestContentionTimeOnWrites

This test intentionally adds sleep time with an active write so that we
can measure contention. Under duress, this can lead to WriteTooOld
errors, so skip the test under duress.

Fixes: #153394
Release note: None

Author: mw5h

pkg/sql/opt/exec/explain/output_test.go

@@ -231,6 +231,8 @@ func TestContentionTimeOnWrites(t *testing.T) {
 	defer leaktest.AfterTest(t)()
 	defer log.Scope(t).Close(t)
 
+	skip.UnderDuress(t, "see issue #153394")
+
 	ctx := context.Background()
 	s, conn, _ := serverutils.StartServer(t, base.TestServerArgs{})
 	defer s.Stopper().Stop(ctx)