Fix stdio permission error in userns container #6885

Job	Run time
test (ubuntu-20.04, 1.22.x, rootless, -race)	7m 24s
cross-i386	1m 2s
test (ubuntu-20.04, 1.22.x, rootless)	7m 13s
test (ubuntu-20.04, 1.22.x, -race)	7m 46s
test (ubuntu-20.04, 1.22.x)	6m 54s
test (ubuntu-20.04, 1.23.x, rootless, -race)	7m 48s
test (ubuntu-20.04, 1.23.x, rootless)	7m 12s
test (ubuntu-20.04, 1.23.x, -race)	7m 55s
test (ubuntu-20.04, 1.23.x)	7m 27s
test (ubuntu-20.04, 1.23.x, criu-dev)	7m 52s
test (ubuntu-24.04, 1.22.x, rootless, -race)	9m 31s
test (ubuntu-24.04, 1.22.x, rootless)	9m 23s
test (ubuntu-24.04, 1.22.x, -race)	7m 40s
test (ubuntu-24.04, 1.22.x)	6m 54s
test (ubuntu-24.04, 1.23.x, rootless, -race)	9m 48s
test (ubuntu-24.04, 1.23.x, rootless)	9m 28s
test (ubuntu-24.04, 1.23.x, -race)	8m 15s
test (ubuntu-24.04, 1.23.x)	7m 44s
test (ubuntu-24.04, 1.23.x, criu-dev)	8m 6s
test (actuated-arm64-6cpu-8gb, 1.23.x, rootless)	11m 30s
test (actuated-arm64-6cpu-8gb, 1.23.x)	7m 51s
all-done	1s
	2h 44m 44s

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