Relax a test to accept `EAGAIN` from `preadv2` on a socket. (#867) #3383

Job	Run time
Check --no-default-features (nightly)	1m 18s
Check selected Tier 3 platforms (nightly)	4m 28s
Rustfmt	7s
Check nightly-only targets (nightly)	34s
Check (stable)	8m 35s
Check (nightly)	9m 17s
Test use-libc (ubuntu)	1m 7s
Check (1.63)	15m 5s
Test use-libc (i686-linux)	1m 34s
Test (ubuntu)	1m 3s
Test (ubuntu-20.04)	1m 4s
Test use-libc (aarch64-linux)	1m 36s
Test (i686-linux)	1m 50s
Test use-libc (powerpc64le-linux)	1m 54s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 53s
Test (aarch64-linux)	1m 33s
Test use-libc (riscv64-linux)	2m 2s
Test (powerpc64le-linux)	1m 34s
Test use-libc (arm-linux)	1m 23s
Test (riscv64-linux)	1m 49s
Test (s390x-linux)	1m 33s
Test (arm-linux)	2m 0s
Test (ubuntu-stable)	1m 18s
Test (i686-linux-stable)	1m 21s
Test (aarch64-linux-stable)	1m 44s
Test (riscv64-linux-stable)	1m 42s
Test (s390x-linux-stable)	1m 35s
Test (powerpc64le-linux-stable)	1m 39s
Test (arm-linux-stable)	1m 31s
Test (ubuntu-1.63)	4m 41s
Test (i686-linux-1.63)	6m 1s
Test (aarch64-linux-1.63)	5m 58s
Test (riscv64-linux-1.63)	5m 34s
Test (s390x-linux-1.63)	4m 59s
Test (powerpc64le-linux-1.63)	5m 5s
Test (arm-linux-1.63)	6m 4s
Test (macos-latest)	1m 21s
Test (macos-11)	1m 9s
Test (windows)	1m 17s
Test (windows-2019)	1m 18s
	1h 57m 36s

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