runtime: raise alert threshold on window smhasher test

This alert is triggering occasionally. I've investigated the
collisions that happen, and they all seem to be pairwise, so they are
not a big deal.  "pairwise" = when there are 32 collisions, it is two
keys mapping to the same hash, 32 times, not 33 keys all mapping to
the same hash.

Add some t.Logf calls in case this comes back, which will help isolate
the problem.

Fixes #39352

Change-Id: I1749d7c8efd0afcf9024d8964d15bc0f58a86e4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/237718


Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>