Golang net: new test TestIPv4WriteMsgUDPAddrPortTargetAddrIPVersion fails on plan9

CL 689976 added a new test which plan9 builders are unable to pass, because function (*UDPConn).writeMsgAddrPort is not supported on Plan 9. Example failure here:

--- FAIL: TestIPv4WriteMsgUDPAddrPortTargetAddrIPVersion (0.01s)
    udpsock_test.go:729: conn.WriteMsgUDPAddrPort(buf, nil, daddr4) failed: write udp 127.0.0.1:62634->127.0.0.1:12345: not supported by plan 9
    udpsock_test.go:733: conn.WriteMsgUDPAddrPort(buf, nil, daddr4in6) failed: write udp 127.0.0.1:62634->[::ffff:127.0.0.1]:12345: not supported by plan 9
FAIL
Running goroutines:
net.(*Dialer).dialCtx.func1()
    /home/swarming/swarming2/.swarming/w/ir/x/w/goroot/src/net/dial.go:577 +0x88
created by net.(*Dialer).dialCtx in goroutine 75
    /home/swarming/swarming2/.swarming/w/ir/x/w/goroot/src/net/dial.go:576 +0x270

FAIL    net 39.467s

Comment From: gopherbot

Change https://go.dev/cl/696095 mentions this issue: net: skip TestIPv4WriteMsgUDPAddrPort on plan9

Comment From: millerresearch

@gopherbot please consider this for backport to 1.24 and 1.25

CL 689976, which caused this issue by breaking the plan9 gotip builders, has been backported to 1.24 and 125. So the plan9 builders for those branches are now broken too.

Comment From: gopherbot

Backport issue(s) opened: #75356 (for 1.24), #75357 (for 1.25).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

Comment From: mrkfrmn

This seems reasonable as its test-only.

Comment From: gopherbot

Change https://go.dev/cl/704279 mentions this issue: [release-branch.go1.24] net: skip TestIPv4WriteMsgUDPAddrPort on plan9

Comment From: gopherbot

Change https://go.dev/cl/704280 mentions this issue: [release-branch.go1.25] net: skip TestIPv4WriteMsgUDPAddrPort on plan9