add a cap to iterations for newenemy test

occasionally the number of iterations picked will take longer than the
timeout for the test suite. capping it means that we sometimes will not
run the full iterations to be convincing, but the effect should be
amortized over PR runs. The cap (and timeout) can be removed for any
change that we suspect may have implications for the test.

e2e/newenemy/newenemy_test.go

@@ -139,7 +139,9 @@ func TestNoNewEnemy(t *testing.T) {
 
 	samplestddev := stddev / math.Sqrt(float64(sampleSize))
 	// how many iterations do we need to get > 3sigma from the mean?
-	iterations := int(math.Ceil(3*stddev*samplestddev + mean))
+	// cap max_iterations to control test runtime
+	const max_iterations = 100
+	iterations := int(math.Max(max_iterations, math.Ceil(3*stddev*samplestddev+mean)))
 
 	t.Logf("check spicedb is protected after %d attempts", iterations)
 	// *6 to cover the worst case where all requests are handled by the slow node