net: skip TestDialCancel on darwin-arm64

net: skip TestDialCancel on darwin-arm64

We're turning up Macs in a network environment that clashes with this
test. I don't think it's critical to get it working, so skip it.

For #49149.

Change-Id: I925e3ecc5356c4cefd208bdcff3d98021215d0b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/402181
Reviewed-by: Alex Rakoczy <alex@golang.org>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Auto-Submit: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>