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>