Flaky UDP test in CI

[squeek502]

Some CI runs have been failing with:

Uncaught Error: ./tests/test-udp.lua:229: EBUSY: resource busy or locked
stack traceback:
	[C]: in function 'assert'
	./tests/test-udp.lua:229: in function <./tests/test-udp.lua:201>
	[C]: in function 'luv.run'
	./lib/tap.lua:61: in function <./lib/tap.lua:48>
	[C]: in function 'xpcall'
	./lib/tap.lua:48: in upvalue 'run'
	./lib/tap.lua:146: in function 'lib/tap'
	tests/run.lua:23: in main chunk
	[C]: in ?

The assert that's failing is

luv/tests/test-udp.lua

Line 229 in b32cc4d

assert(not err, err)

Only seen on macos-latest so far, unsure if it affects others.

[zhaozg]

Manually re-run fails jobs will ok.
It's better better call it again when got EBUSY.

[squeek502]

Note that the test is based on https://github.com/libuv/libuv/blob/v1.x/test/test-udp-multicast-join.c which doesn't seem to have this problem.

[zhaozg]

Maybe later I will do some analysis and testing. now we just skip it.